THE SCATTERING OF HYDRIDE AND HYDROXYL IONS IN OXYGEN
CHARLES EDWARD BAKER
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA August, I960
The author is grateful to Dr. E. E. Muschlitz, Jr., Chairman of his Supervisory Committee, for his assistance, advice and encouragement in the carrying out of this research. He also wishes to thank the other members of his Supervisory Committee for their helpful suggestions in the writing of this dissertation as well as Dr. P. Mahadevan and Mr. William P. Sholette for their assistance in obtaining the experimental data.
The author is indebted to the U. S. Office of Naval Research for the assistantship which they provided and for the financial support of this research.
TABLE OF CONTENTS
ACKNOWLEDGMENT ................. il
LIST OF TABLES................. iv
LIST OF PLATES AND FIGURES........... v
I. INTRODUCTION .............. 1
II. DESCRIPTION OF APPARATUS ........ 8
III. EXPERIMENTAL METHOD .......... 18
IV. RESULTS AND DISCUSSION......... 28
V. SUMMARY................ 49
APPENDIX A DERIVATION OF THE RELATION
AP [(m2 + m^/fo^AE...... 51
APPENDIX B ORIGINAL DATA........... 55
LIST OF REFERENCES............... 59
BIOGRAPHICAL SKETCH .............. 62
LIST OF TABLES
I. Energy values for calculation of AE in
equations (IV.3) (IV.12) ....... 39
II. Total cross section data for 0H~ in 02 55
III. Inelastic cross section data for OET in
IV. Total cross section data for H~ in Og 57
V. Inelastic cross section data for H~ in
LIST OF PLATES AND FIGURES
I. THE SCATTERING ELEMENTS...........12
1. Schematic diagram of negative ion scattering
apparatus ................. 9
2. Schematic diagram of geometry of scattering
3. Comparison of electron detachment and charge
4. Effect of retarding potential on current to
grid at relatively high ion energy .... 31
5. Effect of retarding potential on current to
grid at low ion energy...........32
6. Variation of total scattering cross sections
with ion energy..............34
7. Variation of inelastic scattering cross sec-
tions with ion energy...........35
8. Logarithmic plot of elastic scattering data
for OH* ions in 02............44
Collisions between particles are classified according to whether they survive the collisions with or without an exchange of internal energy. If no change in internal energy is involved then the collision is elastic; otherwise, the collision is inelastic. Inelastic collisions may involve a rearrangement or exchange of the atoms composing the colliding particles or they may merely result in an exchange of energy between them. For each type of collision process a collision cross section may be defined which is a measure of the probability that the given process will take place. The value of these cross sections is dependent on the nature of the forces between the participating particles, their relative velocity and on the amount of energy, if any, exchanged in the process.
The following equations are illustrations of some of the more common inelastic processes that take place when low-energy (<400 ev) negative ions collide with molecules:
X" + Y
X + Y + e
X" + Y
X + Y~
XY- + Y
X- + Y
X" + Y*
X + Y~ + Y
Eq. (1.1) is an example of electron detachment, Eq. (1.2) electron charge exchange, Eq. (1.3) an ion-molecule reaction, Eq. (1.4) excitation of the target molecule and Eq. (1.5) dissociative charge exchange. The processes shown in Eqs. (1.4) and (1.5) generally are important only above an incident ion energy of 50 ev. In each of the first three processes illustrated a negatively charged particle is produced which has an energy much lower than that of an ion that has been scattered elastically. Because of this difference in energy of the charged particles produced by the two types of scattering it is possible to separate the elastic from the inelastic scattering.
The scattering of beams of either charged or neutral particles is a valuable research tool since it provides a direct method for studying the reactions and interactions of particles. Ordinary methods for studying the forces between particles involve the measurement of macroscopic properties such as diffusion and viscosity, which depend on these forces. A well-founded theory is then necessary to relate these forces to the measured bulk properties. For a chemical reaction to take place, the reactant particles must collide in an inelastic collision. If chemical reactions are ever to be completely understood a great deal of information about the nature of particle collisions and of the forces between the
colliding particles must be obtained. Scattering experiments provide the only direct means of obtaining this knowledge.
The first precise measurements of the scattering of low-velocity ions were made by Russell, Fontana, and Simons1 in 1941. Their work involved the scattering of positive ions (H+, H2+, and H2+) in a variety of gases. However, it was not until the past decade that extensive work with negative ion beams was undertaken. The main reason for this is that it is very difficult to produce beams of negative ions of an intensity sufficient to carry out scattering experiments. The processes of negative ion formation are much less probable than the corresponding processes of positive ion formation. Moreover, negative ions are, in general, relatively fragile entitles.^ in addition, the most stable negative ions are formed from atoms and molecules of high electron affinity and hence high chemical reactivity, e.g., oxygen and the halogens. As a consequence of the above, precise experimental work with negative ions could not be undertaken until new and improved apparatuses and techniques were developed.
The importance of the role of negative ions in various scientific fields more than offsets the difficulties encountered in obtaining the experimental data. Mass spec-troscopists are interested in negative ions since they
have found that the negative ion spectra of complex molecules are sometimes simpler and yield more information than the corresponding positive ion spectra.3 High temperature studies of atmospheric gases have been extended to the range in which negative ion formation influences the thermodynamic properties of the gas. Of course, the role of negative ions in astrophysics, particularly the ionosphere and the atmospheres of the sun and stars, has been the subject of a great deal of both experimental and theoretical work, expecially since the advent of space exploration and thermonuclear research.
One of the most remarkable cases in which negative ions play a determining role in the production of an observable phenomenon is that of the solar continuous spectrum.* It has been conclusively demonstrated that the absorption of the negative atomic hydrogen ion, H~ present in the solar photosphere, determines the spectral distribution of the light received by the earth from the sun. Also, the density of electrons in the earths upper atmosphere has a great influence on radio communica-
tion. Electrons are readily produced by photo-ionization of negative ions (X~ + bV* X + e). Hence, the limiting electron density depends on the relative efficiency of processes which remove electrons.
Negative ions are important in connection with problems of atomic and molecular structure. Calculations of electron affinities of atoms and molecules as well as the energy necessary to detach electrons from negative ions have challenged the methods of quantum mechanics. These calculations are complex even for the simplest negative ion, BT, since the solution of a three-body problem is involved. The first detailed calculations of this type were made by Hylleraas6 on the ground state of the H~ ion. His results showed that the undisturbed atomic field of the hydrogen atom is not quite strong enough to produce a stable negative ion. However, when one takes into account the strong interaction between the electrons, which greatly modifies the charge distribution, it is found that each electron moves in an effective attractive field of sufficient intensity to give a total binding energy greater than that in the neutral atom. One of the most accurate values calculated for the electron affinity of the hydrogen atom is that due to Henrich,7 who obtained a value of 0.7466 ev. Detailed calculations for other negative ions are lacking due to the extreme complexity of the problem. However, it is felt that the development of high speed electronic computers will enable theoreticians to eventually calculate the ground state energy of many negative ions. Knowing this energy, the electron affinity of the parent atom or molecule can readily be obtained.
As was previously mentioned, the scattering of beams of low-velocity ions is, in principle, one of the simplest methods for obtaining information about ion-molecule interactions. From the variation of the elastic scattering cross section with ion energy, an ion-molecule interaction potential can be determined and the nature of this interaction may be deduced. The interaction may involve only physical forces such as the polarization of the target molecule by the incident ion. However, if there is a tendency toward compound formation between the colliding ion and molecule (H* in H2 and He), then valence forces become involved in the interaction. A greater understanding of ion-molecule reactions is necessary for elucidation of the mechanisms involved in the reactions taking place when a gas is subjected to radiation. The radiation produces a large number of ions which then undergo ion-molecule reactions to give a variety of products.
This dissertation concerns the measurement of the total and inelastic cross sections of low-energy H~ and OH" ions in oxygen. The elastic cross section is obtained from the experimental results by subtracting the Inelastic cross section from the total cross section. The results for inelastic scattering will be discussed in terms of the possible inelastic processes taking place. From the
observed variation of the elastic scattering with incident ion energy, a potential law for the ion-molecule interaction will be calculated.
CHAPTER II DESCRIPTION OF APPARATUS
The negative ion apparatus used to make the scattering cross section measurements is essentially the same as that described by Muschlitz, Bailey and Simons.8 It consists of five vacuum chambers: the ion source, fore chamber, magnet chamber, post chamber, and scattering chamber, with auxiliary equipment for pumping, gas handling and measuring ion currents and gas pressures. A highly schematic diagram is shown in Fig. 1. The negative ions are produced by the electron bombardment of a gas jet entering at N. The resulting ions, along with some electrons, are drawn into the focusing elements, FE, of the fore chamber where they are collimated into a well-defined beam by electrostatic focusing. The beam then enters the magnet chamber, M, which is located between the poles of an electromagnet. Here electrons and negative ions of undeslred mass are removed and ions of a desired mass emerge and pass into the post chamber where they are collimated by the focusing elements in this chamber and by the defining can, D. The beam which passes into the scattering chamber is well-collimated, of a constant charge to mass ratio and reasonably mono-energetic. Cylindrical ion-beam symmetry
AMPLIFIERS I and 2
POWER SUPPLY 400v DC
Fig. 1. Schematic diagram of negative ion scattering apparatus.
is maintained throughout the apparatus. Ion scattering measurements can be made through the energy range 4-350 ev.
The ion source was designed so that a steady beam of negative ions of the maximum possible intensity could be obtained. The filament is made of iridium, coated cata-
phoretically with thoria. This type filament aids in satisfying the primary objective of high beam intensity. Water vapor was used as the source gas for both the BP and OH"* ions since it gives a higher intensity of H" ions than does hydrogen itself. The water vapor was obtained from a bulb containing carefully degassed distilled water at a temperature of -2 to -7C, depending on the ion and the beam intensity desired.10 The temperature was maintained by use of an acetone-dry ice mixture in a Dewar flask. Since small changes in the backing pressure affect only the total current rather than the ratio of scattered to unscat-tered current, it was not necessary to keep the water bulb at an exact temperature.
Electrostatic ion focusing both in the fore and post chambers was accomplished by a series of coaxial 1/4 in. cylinders surrounding the beam. Each focusing element is connected to an external voltage divider (Fig. 1) and focusing is accomplished by adjusting the potentials on the elements for maximum negative ion current to the collector, C.
The mass spectrometer used in obtaining the desired negative beam is similar in construction to that used by Nier.11 The pole pieces are cut to produce a 90 sector-shaped field. The radius of curvature of the path of ions entering normal to the field is 6.50 cm. Although high resolution is sacrificed in order to obtain higher ion intensities, the mass resolution is, nevertheless, sufficient to separate 0~ and OH" ions.
The ion beam which emerges from the magnet chamber is refocused by four more of the cylindrical focusing elements previously described. After passing through the defining can, D, the beam then enters the scattering cylinder, SL, which contains oxygen at a pressure range of 1-4 x 10""3 mm of Hg. A photograph of the scattering elements is shown in Plate I, and a schematic diagram of the geometry of the scattering elements is given in Fig. 2. All of the scattering elements as well as the focusing elements and the interior surfaces of the magnet are heavily gold plated. This is done in order to prevent interferences from electrostatic charges that build up on oxide-coated surfaces.
The pressure must be kept low in the magnet and post chambers so that the ion beam is not diminished due to scattering in these regions. Since gas enters both the ion source and the scattering chamber, it is essential that considerable pumping speed be provided. This is achieved by using a differential pumping system of four high-speed
THE SCATTERING ELEMENTS
mercury-vapor pumps connected to the first four vacuum chambers through liquid air traps. These pumps are backed by a fifth two-stage mercury pump and a two-stage mechanical pump.
The main difference between the apparatus used for this work and that used previously lies in the geometry of the scattering elements shown in Fig. 2. The left hand side of this figure illustrates the geometry previously used.In order to separate the negatively charged particles produced by inelastic scattering from the elasti-cally scattered ions, an negative potential was placed on S, the scattering cylinder wall and a positive potential on SL, the scattering cylinder lid. However, this method proved unsuccessful since the ion beam was affected by the draw-out field. The present design, shown on the right hand side of the same figure, was adapted from that used by W. H. Cramer13 in his studies of positive ion collisions in gases. A cylindrical grid, shown by the dotted lines, surrounds the beam axis. This grid consists of eight vertical 5 mil gold wires, supported from the plates, G. The extension to the collecting cylinder, C, located inside the grid and concentric with it, was necessary to prevent elastically scattered ions from striking the plate G, just above the end of the scattering cylinder, S. A retarding potential of a few volts sufficient to repel low-energy negatively charged particles produced by inelastic processes
Ion Beam Ion Beam
Fig. 2. Schematic diagram of geometry of scattering elements.
will not appreciably affect the higher energy elastically scattered ions. Hence, the elastically scattered ions are collected on S, and the particles resulting from inelastic scattering are collected on the grid, G, which is positive with respect to S. With the extension present, the scattering path length,/ is 1.639 cm, which is about one-half the distance previously used. The total cross section is the sum of the elastic and inelastic cross sections. Hence, no separation of the two processes is require to measure this quantity and the retarding potential is not necessary. For this same reason, the extension to the scattering cylinder was not required. Without this extension,/ 3.559 cm and n.// 0.07884 cm, and the elastic scattering is measured at about the same limiting angle as previously used.
There are two main advantages of the new geometry over the old. These are: (1) the scattering takes place in a field-free region and (2) the retarding potential has a negligible effect on the elastically scattered ions except at the very lowest ion energies. There is one disadvantage in that charged particles formed by inelastic collisions that have appreciable momentum in the forward direction will not be counted. Nevertheless, inelastic cross sections obtained using the new geometry agree with the previous
results1** for the scattering of H~ ions in Hg to within 5% except at the very lowest energies, where the present results are higher.
Measurements of the current to the grid and collecting cylinder were made using two D.C. unity feedback amplifiers described by Searcy,15 the design of which is based on that of Nier.11 Their maximum full scale sensitivity is 5 x 10"^ amperes using an input resistance of 1011 ohms. Current to the scattering cylinder was measured with a Cary vibrating reed electrometer, Model 31. Weston Model 931 meters, 0-100 microamperes full scale, were used to measure the output of the amplifiers.
Oxygen used as the scattering gas was generated elec-trolytically from a solution of 5% Ba(0H)g using platinum electrodes. In order to remove any impurities from the oxygen, the gas was passed over a hot platinum wire (to catalyze water formation between the oxygen and any hydrogen present), silver foil (to catalyze peroxide and ozone decomposition), and finally phosphoric pentoxide (to remove water vapor present) before it entered the scattering chamber through a capillary leak system. The oxygen pressure in the scattering chamber was controlled by means of three capillaries of varying lengths through which the scattering gas could be pumped. Using these, a pressure range of from 1-7 x 10"3 mm of Hg could be obtained.
The pressure in the various chambers of the apparatus was monitored by an ion gauge, R.C.A. type 1949. Scattering gas pressures were measured with a carefully calibrated McLeod gauge. This is a double gauge of approximately 500 cc capacity, with 1 mm diameter constant bore capillary tubing used in construction. A small Cenco cathetometer which could be read to 0.001 cm was used to measure the difference in mercury levels between the open tube and the closed capillary. These pressure measurements have an estimated accuracy of + 0.5% in the pressure range used.
CHAPTER III EXPERIMENTAL METHOD
General Experimental Procedure
Before a series of experimental measurements can be made using the apparatus described, the system must be pumped down to a pressure of about 2 x 10~5 mm of Hg as indicated by the ion gauge. Not only does this remove any residual gas but also gives assurance that the system is free of any significant leaks. During this pumping period the power supplies, voltage regulators and amplifiers are allowed to warm up so that their stability will be at a maximum. When the required pressure is reached, water vapor is introduced into the source chamber and the filament slowly heated until the electron current to the anode reaches about 1 ma. At this point, the magnetic field is adjusted until the desired ion beam is obtained. It is then focused for maximum ion intensity to the collector by varying the magnetic field and adjusting the focusing elements.
The data for the total cross sections are taken in the following sequence. The currents to the grid, scattering cylinder, and collector are read on the meters with the pressure in the scattering chamber at its minimum
value, that is, about 2 x lO**5 mm of Hg. For these readings, the voltage on the scattering cylinder, V which determines the ion beam energy, is set at a particular value. Oxygen is then introduced into the scattering chamber and allowed to come to equilibrium. The set of current measurements are then repeated. From these data the quantity, RT, the ratio of the current to the collector, C, with all the elements at the same potential (the "unscattered" current) to the total current, can be calculated. Similarly, R^, is this same ratio when the pressure in the scattering region is at its minimum value.
The ion energy is then varied by changing V and the beam is refocused by adjusting the focusing elements. The current measurements are repeated at this new ion energy. The pressure is then determined by taking the average of at least three readings on the McLeod gauge. The temperature to the nearest 0.1C is also recorded. Then the scattering chamber is pumped out and RT at this new energy is determined just as it was previously except that the beam is not refocused, since the same set of focusing conditions must prevail during the determination of both RT and RT. It is apparent that this procedure provides one with data for two different ion energies while requiring only one pressure reading. This is quite advantageous since these pressure readings are often time consuming.
The data for the inelastic cross sections are taken in a very similar fashion except that a retarding potential is now placed on the scattering cylinder, S (see Fig. 2). The ratios are first taken with zero retarding potential. The potential is then increased in 1-volt steps up to a maximum of 8 volts.
At the conclusion of a series of scattering measurements, or whenever the particular negative ion making up the ion beam is changed, it is necessary to perform an energy analysis since the difference between the potential
on the scattering cylinder, V and the actual ion energy,
W, is not constant. However, this difference, AV, is generally about 50 volts, since the ions are formed in a region which is at a potential of +50 volts. The energy analysis is accomplished by setting Vg to 51 volts and then focusing the beam on the defining can lid (D in the schematic diagram) which is connected to an amplifier used exclusively for this analysis. The value of is found for which the maximum current is obtained. This beam includes even the ions of lowest energy. Vg is then decreased in 1-volt steps until the current goes to zero, which is the point at which even the most energetic ions fail to reach the defining can lid. By plotting current vs Vg and
taking the value of V at the half-maximum an average value
for the potential at which the ions are formed is obtained.
This energy analysis indicates a maximum energy spread in the beam of +2 ev. At the conclusion of a series of experimental measurements the apparatus is pumped down and slowly filled to a pressure of one atmosphere with nitrogen dried over glass-wool at liquid air temperature. Treatment of Data
The total scattering cross section for 1 cc of gas molecules at 1 mm pressure and 0C is designated by aT (cm*"1). It is related to the conventional designation for cross section, oT(cm2), by the relation:
aT NoT (III.l)
where N is 3.536 x lO1^, the number of atoms or molecules in the scattering gas per cm3 at 0C and a pressure of 1 mm of Hg. aT can be calculated from the data obtained by the previous procedure by the relation:1*5
aT p PQ lQgiO RT (I". 2)
2.303(273.2 + TC) 273.2 /
is the scattering path length and pQ is the lowest pressure attainable in the scattering chamber. The ratio RT has already been designated as:
R *C (III.3)
where 1^, 1^, and Ig are the measured currents to the collector, grid,and scattering cylinder, respectively.
The inelastic cross section, aj, can also be calculated from the experimental data using the equation:
a -S-2- aT (III.4)
Rrp RT 1
where RQ is the ratio of the current to G with a retarding potential on S (the inelastically scattered current), to the total current entering the collision chamber, and Rq is the same ratio without gas in the scattering chamber, RT, RTo andaT have their usual significance. This relation is effectively the fraction of the scattering which is inelastic times the total scattering cross section.
Since the total cross section is the sum of the inelastic and elastic cross sections, the elastic cross section, ag, can be calculated from the relation:
aS aT al' (III. 5)
As was mentioned in the introductory chapter, it is possible to derive interaction potentials from the variation of the elastic cross section with ion energy. Three primary assumptions are made in this treatment. The target particle is assumed to have a negligible initial momentum compared to the incident momentum of the ion; the collisions measured by aq are assumed not to involve changes in the
internal energy of either particle; and finally, the force of interaction is assumed to be a function only of the distance between the two particles.
Since ions scattered through small angles where diffraction effects would be expected reach the collecting cylinder and are, therefore, not counted as scattered, classical theory can be used for the analysis of the elastic cross section data. However, these scattering cross sections are smaller than the true cross sections which would Include all of the small angle scattering.
If a potential function of the form V + K/rn is assumed, where the minus sign refers to attraction and the plus sign to repulsion, a relation may be derived which expresses the measured ag as a function of the ion energy, W. The parameters K and n may then be evaluated from this relation using the experimentally determined values of ag at various ion energies. An exact derivation of this relation requires a laborious graphical integration for each
value of the ion-molecule mass ratio, m^/mg.17 However, an
approximate treatment by KellsA gives results which agree with the exact treatment to within 1%. If this approximate method is used the desired relation expressing ag as a function of W may be derived.8 The resulting expression is:
KClN2/n [~ 1
The plus sign in the expression for Q corresponds to an attractive potential law, and the minus sign corresponds to a repulsive potential law.
If log ag is plotted against log W a straight line will result if the data can be expressed in terms of the assumed potential function. The constants K and n in the potential function may then be evaluated from the intercept and slope of this line.
Under the assumption of a simple inverse power potential there is a distance of closest approach, rQ, for each ion energy such that if an ion fails to approach the scat-terer within this distance, it will not be counted as scattered. That is, it will arrive in the collecting cylinder. This distance, averaged over the scattering path length, is found from the relation:16
log ag ~ log W + log Q. (III.7)
In the above expression ag, W, n, K and N have the same designation as before while m^ is the mass of the incident ion,yx is the reduced mass,./ the length of the scattering region, and a the radius of the collecting cylinder aperture. C is given by:
n + 2 vwa
A scattering apparatus cannot determine whether a beam particle has been scattered by attraction or repulsion. Since a single-term potential function is being used, one must therefore assume either attraction or requlsion in calculating the interaction potential. This will not affect the value of the exponent n but it will affect the magnitude of K.
At sufficiently large values of the internuclear distance an attraction due to the polarization of the target molecule by the incident ion would be expected. Similarly, for very small values of the internuclear distance repulsion would predominate. However, there exists an intermediate range of nuclear separation for which the single-term potential function is inadequate due to the presence of both attractive and repulsive forces. This suggests that one should assume at the beginning a potential function such as:
which includes both a repulsion term and an attraction term. However, a general treatment of the scattering problem using a potential function similar to the above would be much more complicated mathematically than the treatment using a one-term potential. Furthermore, it is only possible to adjust two parameters on the basis of the
experimental results. Thus, two of the four parameters of the two-term potential must be assumed. The remaining two can then be determined from the experimental data.
This type of treatment is mathematically formidable ex-
cept possibly for integral values of m and n. Also, this method is of little value when there are no grounds on which to base the assumption of two of the parameters involved.
In most of the previous work on the low-energy scattering of negative ions,8*12'14 the potential functions have been calculated assuming an attractive interaction. Mason and Vanderslice20 have shown, however, that it is not correct to attribute.the interaction to purely attractive forces even at the lowest incident ion energies used in this work. Nevertheless, for cases in which chemical binding are clearly involved, attraction predominates at low energies and assumption of an attractive potential seems reasonable.
Despite the fact that there is some ambiguity as to whether one should attribute the scattering of an ion to attractive or repulsive forces, the work of Mason and Vanderslice20 shows that the scattering measurements obtained in this type experiment are in essential agreement with independent quantum-mechanical estimates
of the intermolecular forces involved. Thus, this method of relating measured cross sections to molecular forces is correct.
CHAPTER IV RESULTS AND DISCUSSION
In order to demonstrate that the new scattering elements could separate the slow charged particles due to inelastic processes from the relatively energetic elastically scattered ions, a study was made of the effect of the retarding potential on the ratio R The results of this
work are shown in Figs. 3 through 5. Figure 3 shows a comparison of this effect on the scattering of Hg+ in Hg, where charge exchange plays a predominent role, and on H~* in Hg for which the inelastic process is probably entirely electron detachment. It is seen that in both cases a saturation value is reached indicating that all the slow particles have been repelled from the scattering cylinder wall and collected on the grid. For H2+ in Hg saturation is reached at a value of about +0.5 volt, indicating that the positive ions formed by the charge exchange process have approximately thermal energies. However, -2.5 volts are needed to produce saturation for H" in Hg case. It may therefore be concluded that these detached electrons have energies significantly higher than thermal, possibly as great as several ev. These results show that not only can one separate the inelastic croBS section from the elastic by a
Fig. 3. Comparison of electron detachment and charge exchange.
retarding potential method (and thereby determine the inelastic cross section), but that information as to the energy and hence kinds of particles produced can also be obtained.
The retarding potential curves for H~ in 02 and OH" in 02, both at an ion energy of 150 ev, are shown in Fig. 4. Figure 5 gives results for the same two systems at an ion energy of 15 ev. For H" in 02 saturation occurs at about 1 volt for both ion energies. This indicates that slow negatively charged particles are produced in these collisions rather than "fast" electrons as was the case with H~ in H2. For OH" in 02 saturation occurs at a retarding potential of about 4 volts at an ion energy of 150 ev. However, at an ion energy of 15 ev, the retarding potential curve does not quite flatten out due to a small effect of the retarding potential on the elastically scattered ions. The high value of the retarding potential necessary to produce saturation is indicative of the presence of energetic electrons produced by electron detachment.
The data from which the total and inelastic cross sections for the scattering of OH" and H" in 02 were calculated are tabulated in Appendix B. Figures 6 and 7 are a graphical presentation of these data.
The total cross sections for the scattering of H~ and 0H~ in 02 as a function of the energy of the incident ions
W= 15 0V
0.0 -2.0 -4.0 -6.0 -8.0
Fig. 5. Effect of retarding potential on current to grid at low ion energy.
are shown in Fig. 6. Figure 7 shows the variation of the inelastic cross section with ion energy for the same two systems. Since the scattering cross sections for OH" in 02 have not been measured by other investigators, a comparison of the results cannot be made. The cross sections for
the low-energy scattering of H~ in 02 have been previously
measured by McGuire. The total cross section data shown
in Fig. 6 are in good agreement with his results. However,
the inelastic cross sections obtained in this research are
significantly larger than those obtained previously. The
earlier results are much too small due to the inefficient
separation of the inelastically scattered particles from
those scattered elastically.
There is a very striking similarity between the curve
for H~ and the curve obtained by Muschlitz for 02~ in 02<22
The main difference between these two curves is that the
maximum and minimum are more pronounced and occur at a
higher energy for the H~ in 02. Likewise, the resulting
curve for OH" is very similar to that for 0" in 02 and also to that for H" in the rare gases.8 In these cases the curve tends to zero as the ion energy is decreased, but the appearance potential seems to be lower for OH" than for 0- in 02.
The most significant feature of the otj vs ion energy curve for H" in 02 is that the cross section does not go
Fig. 6. Variation of total scattering cross sections with ion energy.
I I 1 I__I_1 I
0 5 10 15 20
(ION ENERGY, ev)"2
Fig. 7. Variation of inelastic scattering cross sections with ion energy.
to zero as the ion energy is decreased. According to the "adiabatic theory" of H. S. W. Massey23 the probability of an inelastic collision occuring will be small if:
-nT1>>l (IV. 1)
where a is the range of interaction between the particles involved, that is, the collision radius; v is the relative velocity of the particle; AE is the energy change or defect in the collision; and h is Planck's constant. The theory says, in effect, that since the particles are approaching each other with a velocity which is small compared to the velocity of the electrons in the particles, these electrons have plenty of time to readjust themselves to the slowly changing conditions without a transition taking place. According to this theory the inelastic cross section will be small unless AE is very small. In a symmetric charge exchange process such as
02- + 02 -02 + 02~, (IV. 2)
where the particles separating after the collision are in their ground states, the energy defect is zero and appreciable inelastic cross sections would be predicted even at ion energies of only a few electron volts. This theory is supported by the results of Muschlitz for the inelastic cross section of 02~ in 02, to which reference has already be made.22 The cross section shows no tendency to go to
zero with decreasing ion energy. On the contrary, it appears to be rising as the ion energy goes to zero. Also the retarding potential data for 0g" in Og indicate that the inelastic process is one which produces slow charged particles. This is indicative of charge exchange rather than electron detachment.
Since there is a striking similarity between the results for H" in 02 and 02" In 02, it is reasonable to expect that there is some inelastic process which has an energy defect essentially zero which is causing the curve to rise as the ion energy approaches zero. Some possible reactions for this system are:
IT + Og -? H + 02 + e AE 0,75 ev* (IV.3)
H~ + Og - H + 0g~ AE 0.60 ev (IV.4)
H~ + Og -^ OH" + 0 AE -0.7 ev (IV.5)
H~ + 0g -* OH + 0- AE 0.05 ev (IV.6)
The AE values for these equations and also for Eqs. (IV.7) through (IV.12) were obtained using the data for dissociation energies and electron affinities listed in Table 1.
Since the retarding potential curves for this system indicate that slow negatively charged heavy particles are produced in the inelastic collisions, the first reaction cannot be expected to be contributing significantly to the low-energy cross section. The charge exchange reaction
?Computed with all particles in the ground state.
[Eq. (IV.4)] is endothermic by 0.60 ev which differs considerably from an energy defect of zero. Thus it is probable that the last two reactions are making the major contributions to the low-energy inelastic cross section. The last reaction has an energy defect which is nearly zero, hence it would be expected to make a significant contribution to the cross section down to ion energies very close to zero. However, the exothermic ion-molecule reaction, Eq. (IV.5), is probably making the major contribution at very low ion energies since the excess energy of 0.7 ev may readily be taken up as vibrational energy in the OH"* ion produced by the reaction. The result of this is an energy defect that is effectively zero.*24 This is due to the fact that the vibrational levels in the OH" ion are about 0.4 ev apart. Hence, excitation of the ion to the second vibrational level would require about 0.8 ev which is quite close to the excess energy involved in this reaction.
As was previously mentioned, the variation of the inelastic cross section for OH*" in 02 with ion energy is quite similar to that of HT in the rare gases and to 0" in 02. For the inelastic scattering of these low-energy OH*" ions, the following processes may contribute to the cross section:
TABLE I. Energy values for calculation of AE in equations (IV-3) (IV-12).
energies and Energy in
electron electron Reference
D (02) 5.115 26 Brix and Herzberg
D (OH) 4.35 Herzberg27
D (03) 1.07 Rossini, Wagman, et al.28
D (H02) 2.0 Foner and Hudson/29 Robertson30
EA (H) 0.747 Henrich7
EA (03) 2.88 Pritchard31
EA (OH) 2.2 Pritchard31
EA (H02) 3.0 Pritchard31
EA (02) 0.15 Burch, Smith, and Branscomb32 Mulliken33
EA (0) 1.465 Branscomb, Burch, Smith, and Geltman34
OH" + Og --0H + Og + e AE 2.2 ev (IV.7)
OH" + Og---? OH + 02- AE 2.0 ev (IV. 8)
OH- + 02 -? 03- + H AE 2.6 ev (IV.9)
OET + 02 -* 03 + H" AE 4.01 ev (IV.10)
OBT + 02 -? H02- + 0 AE 1.6 ev (IV.11)
OH" + 02 -? H02 + 0- AE 3.2 ev (IV.12)
Since all of these processes are endothermic, the Inelastic cross section should go to zero as the incident ion energy is decreased. The experimental results indicate that, Indeed, this is the actual case. The retarding potential analysis for this system showed that about 4 volts were required to produce saturation. This indicates the presence of relatively energetic charged particles, that is, electrons, rather than slow heavy ions which saturate at about 1 volt. On this basis, it is concluded that the processes given by Eqs. (IV.8) through (IV.12) do not make a large contribution to the cross section; therefore, the inelastic collisions of OBT in 02 are probably primarily electron detachment collisions as shown in the first equation.
The "appearance potential" (AP) for a given inelastic process is the minimum ion energy at which the inelastic process occurs. If momentum is to be conserved in the collision, the "appearance potential" must be given by:
(mg + E m2
if the energy and momentum of the electron is neglected. In this equation m^ is the mass of the incident ion, nig the mass of the target molecule, and AE the energy defect for the process. The derivation of this relation is given in Appendix A. Thus, for OH*" striking an oxygen molecule, which is the process for Eqs. (IV.7) through (IV.12),
The lowest AP which would be predicted using this relation is 2.4 ev, which is obtained for the process indicated by Eq. (IV.11). However, the experimental data extrapolates to zero cross section at a value definitely lower than this.
It is interesting to note that this process [jlq. (IV. 11) is also the process for which the AE value is the least certain. The dissociation energies and electron affinities needed to calculate the energy defect for the first four processes are known reasonably accurately with the possible exception of the electron affinities of 02 and O3. Recent experimental results and theoretical considerations33 give good support to the value for the electron affinity of Og of 0.15 ev as listed in Table I. It seems unlikely that the electron affinity of 03 is higher than the value given by Pritchard31 of 2.88 ev. However, there is considerable doubt as to the reliability of the electron affinity for
H02, listed by Pritchard as 70 kcal/raole (3.0 ev) and of the energy evolved in the reaction:
H + 02 -> H02. (IV.15)
The value of 2.0 ev used for D(H02) in calculating the AE value for Eq. (IV.11) was obtained first by Robertson30 and later by Foner and Hudson29 using an electron impact technique. However, the latter point out that their agreement with Robertson is fortuitous since different values for the AP of H02 from H202 where obtained. Both these results were based on the assumption that the products of the dissociative ionization reaction involved where formed with zero kinetic and excitation energies. Hence, if this were not the case, the value for D(H02) would be higher. In addition, theoretical arguments35 based on atomic and molecular orbital theory and on evidence from interatomic distances have been given to support a value for D(H02) between 2.6 and 3.0 ev.
The value of 3.0 ev for the electron affinity of H02 was obtained by Pritchard using the method of spectral interpolation in conjunction with the heat of hydration of H02". The value for the heat of hydration depends on the effective ion radius and must be considered only an estimate. Thus, this method of obtaining electron affinities must be considered an approximate one only. The first value of the electron affinity of H02 reported was
4.6 ev. This was obtained using a cyclic process which also involved the heat of hydration of the H02~ ion. It is quite evident that there is a large uncertainty at the present time as to the electron affinity of the H02 radical.
The experimental AP is between 0.1 and 0.5 ev, which, on the basis of Eq. (IV.14), indicates that there is a process taking place with a AE value of about 0.2 ev. This process could be that represented by Eq. (IV.11) if the sum of the electron affinity and dissociation energy of H02 were greater by about 1.3 ev (i.e., if[AE 2.2 + 4.35] [6.33 0.25 rather than AE [2.2 + 4.35]] + -3.0 2.0] 1.6). In view of the previous discussion concerning these values a difference of 1.3 ev in this sum seems much more than a remote possibility. Elastic Scattering
Figure 8 is a plot of log W vs log ag for the system OH" in 02 from which the parameters n and K may be evaluated by the method previously discussed. This plot is for the energy range 4.4 to 350.4 ev which represents the entire energy range of the present apparatus. The experimental data are seen to fall quite closely along a straight line which was obtained by the method of least squares. This indicates that the assumptions leading to the interaction potential V + K/rn are reasonably valid throughout this energy range. From the slope and intercept of
the line the following interaction potentials were calculated using Eq. (III.7):
11 5 23 3
V ~ or V + pfTso, (IV-16)
where V is in electron volts and r is in angstroms. The relation on the left represents an attractive potential, whereas the relation on the right is obtained when a repulsive interaction is assumed. For the attractive potential the average distance of closest approach, rQ, ranges from 2. at an incident ion energy of 4.4 ev to 0.84A at an energy of 350 ev. For the repulsive potential, rQ ranges from 2.65A* down to l.OlX for the previous ion energies. If one considers the best straight line through the
low energy points (from 25.7 ev down to 4.4 ev) similar results are obtained. The interaction potentials in this case are:
V - jg&S r V ? (IV-17)
The distances of closest approach for these two potentials are, respectively, 2. and 2.56A for the lowest ion energy (4.4 ev) and either 1.56% or 1.84? for an ion energy of 25.7 ev.
Since there was a striking similarity between the experimentally measured cross sections for OH" in 02 with those for 0" in 02,19 it might be expected that the interaction potentials calculated might also be similar. The following potential function was obtained for 0~ in 02:
The r0 values calculated are 2.5A for an ion energy of 3.0 ev and 1. for an energy of 21.0 ev. The interaction of the 0H~ with 0g in the same energy range is seen to be larger and to have a functional dependence on distance that is quite different, the larger value of n indicating a "harder" interaction. This difference in interaction potential may be due to the fact that chemical binding forces are probably involved in the 0~ case since the O3" ion is stable as indicated by its electron affinity,31 whereas the HO3- ion has not been reported experimentally or postulated as being stable on theoretical grounds.
The elastic cross sections obtained for BT in 02 from the relation ag aT az do not give results which one would expect when the logarithmic plot of ag vs W is made. The best straight line through the data for the energy range 6.0 12 ev gives a value of n of about 24. This value increases rapidly as higher energy points are included, a value of n 68 being obtained for the energy range 6 25.7 ev. It is quite unlikely that this is the true value for the functional dependence of the interaction potential on distance. It is believed that this result is due to a combination of several factors, the main one being the excitation of the 02 molecule to the excited electronic
state, Ag, which has an energy of only about 1 ev above the ground state. This excitation, although an inelastic process, would contribute to the elastic cross section since the scattered ion would retain enough kinetic energy to overcome the retarding potential used for the separation of the products of the two processes. Although this
excitation also occurs with OH*", 0" and Og" in Og, it becomes significant only at energies higher than those for
which the interaction potential is calculated and, hence, does not interfere greatly. However, H" in Og is an extreme case since ET has the least mass of any negative ion. Thus, at a given ion energy its velocity will be much greater than the other ions mentioned since velocity is inversely proportional to the square root of mass. Now, the adiabatic theory jj3q. (IV. 1)] states that the probability of an inelastic collision increases with increasing relative velocity of the colliding particles. Hence, it is quite possible that excitation is occuring in the energy range for which the high exponent was obtained, that is, 6.0 12.0 ev, as well as at higher energies. The situation is farther complicated by the fact that both aT and otj are large for H~ in Og. Hence, Og, which is obtained by difference, is the result of subtracting two large numbers. This makes irregularities in the resulting data. Furthermore, the ion intensity for HH is much less than that for OH" or 0"" and Og"". This makes work at low energies much more difficult.
In view of the previous discussion it should be possible to obtain the true low energy interaction potential by working at energies low enough to preclude any significant excitation of the Og molecule. In the present apparatus measurements below 4 ev are not reliable due to energy spread in the beam. In an attempt to clarify the situation, a short extrapolation was made of the ccj vs W curve from 6.0 ev down to 2 ev. atj values were obtained from this plot and subtracted from the aT curve to get the aS values. The resulting data were plotted logarithmically in the usual manner and a value for n calculated from the slope of the best straight line through these points. This procedure gave a value of n of about 3.0 which is similar to the functional dependence on distance found for the interaction of 0"" in Og.22 Both 03~ and H0g~ are stable molecular ions; therefore, valence forces would be involved in each of the ion-molecule interactions. Thus, it appears that the interaction of BT in Og follows an inverse third power law at low energies but that as the energy is increased the onset of the excitation process precludes an accurate determination of the interaction potential.
CHAPTER V SUMMARY
The total and inelastic collision cross sections for H" and OH" ions in oxygen have been measured for ion beam energies of 4-350 ev. A cylindrical beam of momentum-analyzed, reasonably mono-energetic 0H~ or H" ions, produced by electron bombardment of water vapor, was passed through a scattering cylinder containing the scattering gas at pressures of 1-4 x 10~3 mm of Hg. Elastically scattered ions were distinguished from slow charged particles produced by inelastic collisions by means of a retarding potential applied between a cylindrical grid surrounding the beam and an outer collecting cylinder. From the ratios of the currents to the various scattering elements to the total current, the total cross section, a^, and the inelastic cross section, ctj., were calculated. The elastic cross section, ag, was taken to be the difference
between a and a .
For H~ in Og, a plot of vs ion energy resulted in a curve which did not go to zero as the ion energy was decreased. On the basis of the retarding potential analysis and the adiabatic theory it was concluded that the high cross section at low ion energies was due to the following ion-molecule reactions:
H~ + 02 -? OH" + 0 AE ** -0.7 ev
H" + 02 -*- OH + 0". AE 0.05 ev
For OH" in 02, the inelastic cross section tended to zero as the ion energy was decreased. This would be expected since all of the inelastic processes for this system are endothermic. The retarding potential data indicated that the process making the major contribution to the inelastic cross section was electron detachment.
From a logarithmic plot of ag vs ion energy, a one-term interaction potential for OH" in 02 was calculated. On the assumption of an attractive interaction, the following potential function was obtained:
over the range of interaction 0.84 2.23A, where r is in angstroms and V in electron volts. The repulsive potential calculated was
V = + 23.3 r4.50'
where the distance of closest approach ranged from 1.01-2.65$. It was not possible to accurately determine the interaction potential for H~* in 02 by the method used for 0H~ in 0g. Excitation of the 0g molecule to the low-lying excited electronic state,*Ag, was concluded to be the major interfering factor.
DERIVATION OF THE RELATION Mo + nii AP -~ AE
In this relation, AP is the appearance potential of the process under consideration, m^ is the mass of the incident ion, m2 is the mass of the struck particle, and AE is the energy defect of the reaction.
Consider a head-on collision between a negative ion, A~, of energy W and a target molecule, B2, initially at rest, that results in electron detachment. This process may be represented by:
A" + B2 -? A + B2 + e. (A.l)
Now, if the energy and momentum of the electron is neglected, the following relations must be satisfied in order to conserve energy and momentum in the process:
raivx (StajW)1/2 rn^Vj' + m2v2f (A.2)
W 1/2 m^!2 1/2 mjVj/2 + 1/2 m2v2,2+ Ed (A.3) where v^ and v^f are the initial and final velocities of ml' v2* *s t^ie flnal velocity of m2 and E^ is the electron detachment energy, which is the AE value for this process. Solving for v^ in Eq. (A. 2) yields:
Substituting this value for Vj' into Eq. (A.3) obtain ,_!/ Wl*. Va Va. +Ed. (A.5,
Expanding the term in brackets and then dividing through by l/2m1 yields:
-- ^ i*i*>v* ? ^ ? %
(Si ?) va [S? <^>1/2] v2- + Ed o,
which is a quadratic equation. Hence,
_ /2WN1/2 2m9zW /mo \
2f!!E + Is
Factoring out an m2 from under the radical, dividing both numerator and denominator by m2 and then rearranging, gives:
/2W\l/2 /2\l/2 f 7*l\ w
y I n i ii ... *.......... ........ Hi
Since v2* must be a real quantity,
m2 + ml
Now, the appearance potential, AP, is the minimum value for W for which the given process can occur, and E^ AE; hence,
Ap m2+ ml AE, (A.9)
which is the desired relation. It is clear that this same relation would hold for a charge exchange process for the only difference would be that in this case the difference between the mass of B2 and B2- would be neglected. For a process such as:
A" + B2 -> AB2 + e (A. 10)
the derivation is simplified. In this case, conservation of momentum and energy requires that
mJv1 (2m1W)1/2 m^Vg' (A. 11)
W 1/2 m^!2 1/2 mg'Vg'2 + Ed Eb, (A. 12)
where Eb is the binding energy of AB2,and ra2' is the mass of ABg. Following a procedure exactly analogous to that previously used, obtain
W 1 ra1/m2' m2' (Ed ~ Eb)
rag' *= nij + m2 and Ed Efe AE.
m-1 + Sin
AP m2 (A. 14)
APPENDIX B ORIGINAL DATA
TABLE II. Total cross section data for 0H- in 02.
vs (v) AV (v) W (ev) T (C) (p-po)xl03 (mm of Hg) RT *T aT (cm-1)
400 49.7 350.3 30.1 2.433 .685 .994 47.7
350 49.7 300.3 30.1 2.433 .690 .991 46.4
300 49.7 250.3 30.4 2.435 .695 .997 46.3
250 49.7 200.3 30.4 2.435 .697 .997 45.9
200 49.7 150.3 29.8 2.430 .696 .996 46.0
150 49.7 100.3 29.8 2.430 .663 .948 45.8
140 47.8 92.2 28.8 2.816 .625 .966 48.1
125 49.7 75.3 30.0 2.413 .677 .982 48.1
110 50.1 59.9 29.7 2.087 .711 .981 48.1
100 49.7 50.3 30.0 2.413 .661 .982 51.2
90 47.8 42.2 29.2 2.793 .602 .965 52.5
80 50.1 29.9 29.5 2.076 .676 .964 53.2
75 47.8 27.2 29.2 2.793 .550 .923 57.6
70 50.1 19.9 29.4 2.065 .631 .917 56.3
65 50.1 14.9 29.5 2.076 .649 .970 60.3
60 50.1 9.9 29.4 2.065 .608 .948 66.9
57 50.1 6.9 29.0 2.017 .590 .941 72.0
55 50.1 4.9 29.0 2.017 .551 .928 80.3
53 47.8 5.2 30.0 1.710 .467 .726 80.5
52 47.8 4.2 30.0 1.710 .418 .633 75.6
TABLE III. Inelastic cross section data for OET in 02.
Vs (v) AV (v) W (ev) T (0C) (p-p )xlo3 R R (cm-1) R--R<> Ro R cxT
(mm of Hg) r T T (cm_i}
400 49.6 350.4 31.6 3.244 .780 1.000 52.1 .160 .220 37.9
300 49.2 250.8 33.1 3.352 .774 .987 49.6 .156 .213 36.1
200 50.3 149.7 31.3 3.451 .785 .998 47.2 147 .213 32.6
150 48.8 101.2 27.8 3.621 .780 .997 45.5 .140 .217 29.4
125 48.8 76.2 27.5 3.625 .784 .994 44.0 .137 .210 28.7
110 48.8 61.2 27.8 3.621 .779 .997 45.8 .138 .218 29.0
95 48.8 46.2 27.5 3.625 .776 1.000 47.0 135 .224 28.3
85 49.3 35.7 24.5 3.352 .770 1.000 51.9 .126 .230 28.4
75 49.3 25.7 24.5 3.352 .746 .979 53.9 110 .233 25.4
65 49.2 15.8 32.8 3.345 .745 1.000 60.1 .100 .255 23.6
60 49.6 10.4 31.9 3.298 .724 .987 64.0 .086 .263 20.9
58 49.6 8.4 31.8 3.342 .710 .978 65.2 .091 .268 22.1
56 49.6 6.4 31.8 3.342 .674 .987 77.7 .084 .313 20.9
54 49.6 4.4 32.2 3.384 .663 .962 75.1 .077 .299 19.3
TABLE IV. Total cross section data for H" in o2.
Vs (v) AV (v) W (ev) T (C) (p-po)xl03 RT aT (cm"1)
(mm of Hg) i
400 48.8 351.2 28.1 1.969 .543 .991 94.7
350 48.8 301.2 28.1 1.977 .531 .991 97.8
300 48.6 251.4 28.1 1.912 .518 .994 105.7
250 48.6 201.4 28.1 1.912 503 .994 110.4
210 48.6 161.4 27.9 1.963 .493 .993 110. 5
210 48.6 161.4 28.4 1.915 .494 .994 113.3
190 48.6 141.4 27.9 1.963 .488 .994 112.3
170 48.6 121.4 27.6 2.024 .490 .995 108.3
150 48.6 101.4 27.6 2.024 .492 .991 107.0
130 48.6 81.4 27.4 2.000 .500 .978 103.7
110 48.6 61.4 27.4 2.000 .523 .991 98.8
100 48.5 51.5 29.7 2.096 .524 .982 93.4
87 48.8 38.2 27.0 2.097 .530 .953 86.4
80 48.8 31.2 27.2 2.109 .553 .967 81.9
73 48.8 24.2 27.0 2.097 535 .916 79.2
68 48.8 19.2 27.2 2.109 .568 .988 81.1
65 48.8 16.2 27.1 2.187 .512 .916 82.2
60 48.8 11.2 27.1 2.187 .474 .870 85.7
57 48.8 8.2 27.4 2.093 .487 .894 89.8
55 48.8 6.2 26.6 2.090 .492 .924 93.0
54 48.5 5.5 29.7 2.096 .394 .786 102.7
53 48.8 4.2 27.4 2.093 .396 .808 105.3
51 48.6 2.4 28.4 1.915 .344 .753 126.9
TABLE V. Inelastic cross section data for H" in 02.
vs (v) AV (v) W (ev) T (C) (p-po)xl03 (mm of Hg) Rrji aT (cm-1) Rg-Rg R^ijiRrp I (cm-1
400 48.2 351.8 28.5 2.975 .640 .990 98.8 .215 .350 60.7
300 48.2 251.8 28.5 2.975 .628 1.000 105.3 .227 .372 64.3
200 48.2 151.8 28.7 2.944 .609 .993 112.1 .248 .384 72.4
150 48.2 101.8 29.3 2.884 .607 ,984 113.2 .243 .377 73.0
123 48.3 74.7 28.6 5.130 .473 .993 97.4 .357 .520 66.7
96 48.0 48.0 26.5 3.147 .670 .996 84.4 .209 .326 54.1
88 48.3 39.7 28.6 2.291 .754 1.000 83.0 .148 .246 49.9
75 48.1 26.9 26.8 3.113 .692 .994 77.9 192 .302 49. 5
70 48.3 21.7 28.6 2.291 .756 .989 79.0 .143 .233 48.5
65 48.1 16.9 26.8 3.113 .690 .997 79.3 .189 .307 48.8
60 48.1 11.9 28.0 3.070 .690 .981 77.2 .207 .291 54.9
58 48.0 10.0 26.5 3.147 .652 .995 89.9 .225 .343 59.0
56 48.0 8.0 26.6 3.060 .650 .984 90.8 .209 .334 56.8
54 48.0 6.0 26.6 3.060 .649 .981 90. 5 .231 .332 63.0
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Charles Edward Baker was born November 8, 1931, in Manchester, Kentucky. He attended elementary school in Manchester and in Cincinnati, Ohio, and was graduated from the Berea Foundation School, Berea, Kentucky, in June, 1949. In June, 1953, he received the Bachelor of Arts degree from Berea College, with a major in Chemistry. After working briefly for Monsanto Chemical Company in Dayton, Ohio, he entered the United States Army from which he was discharged in December, 1955. In September, 1956, having accepted an assistantship in the Department of Chemistry, he entered the Graduate School of the University of Florida to work toward the degree of Doctor of Philosophy. In July, 1957, he became a graduate assistant in research in the Department of Electrical Engineering and held this position until July, 1960.
Charles Edward Baker is married to the former Jeanelle Lecky and is the father of two sons. He is a member of the American Chemical Society and of Phi Kappa Phi.
This dissertation was prepared under the direction of the chairman of the candidate's supervisory committee and has been approved by all members of the committee. It was submitted to the Dean of the College of Arts and Sciences and to the Graduate Council and was approved as partial fulfillment of the requirements for the degree of Doctor of Philosophy.
August 13, 1960
Dean, Graduate School
In reference to the following dissertation: AUTHOR: Baker, Charles
TITLE: The scattering of hydride and hydroxyl in oxygen, (record number:
565724) PUBLICATION DATE: 1960
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Please print, sign and return to: Cathleen Martyniak UF Dissertation Project Preservation Department University of Florida Libraries P.O. Box 117008 Gainesville, FL 32611-7008