• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Negative ions
 Scattering
 Description of apparatus
 Experimental procedure
 Treatment of data
 Conclusions
 Appendix
 Bibliography
 Biographical sketch
 Copyright














Title: Scattering of hydride ions in oxygen gas.
CITATION PDF VIEWER THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00091632/00001
 Material Information
Title: Scattering of hydride ions in oxygen gas.
Series Title: Scattering of hydride ions in oxygen gas.
Physical Description: Book
Creator: McGuire, John Murray,
 Record Information
Bibliographic ID: UF00091632
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000559221
oclc - 13447943

Downloads

This item has the following downloads:

Binder1 ( PDF )


Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
    List of Tables
        Page iv
    List of Figures
        Page v
    Negative ions
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Scattering
        Page 6
        Page 7
        Page 8
    Description of apparatus
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Experimental procedure
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Treatment of data
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
    Conclusions
        Page 41
        Page 42
    Appendix
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
    Bibliography
        Page 49
        Page 50
    Biographical sketch
        Page 51
        Page 52
    Copyright
        Copyright
Full Text












SCATTERING OF HYDRIDE IONS

IN OXYGEN GAS











By
JOHN MURRAY McGUIRE


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY











UNIVERSITY OF FLORIDA
January, 1955



















ACKNOWLEDGEME NTS


The author wishes to thank his research director, Dr. E. E.

Muschlitz, Jr., for his advice and assistance in carrying out the

research and writing of this dissertation. He also wishes to thank

Dr. J. H. Simons for his advice and encouragement and Dr. T. L.

Bailey for his help in collecting the data embodied herein. Finally, the

Physics Branch of the Office of Naval Research is thanked for the

Assistantship which the author held during the course of this research.


John Murray McGuire


Gaine ville, Florida

January, 1955
















TABLE OF CONTENTS


LIST OF TABLES . . . . . .

LIST OF PLATES AND FIGURES .....


* . .

* . .


Chapter
I NEGATIVE IONS . . . . . .

II SCATTERING . . . . .... .

III DESCRIPTION OF APPARATUS .......

IV EXPERIMENTAL PROCEDURE .......

V TREATMENT OF DATA . ........

VI CONCLUSIONS ....... .......

APPENDIX . .. . . . . . .

APPENDIX . . . . . .. .
DEFINITION OF SYMBOLS

BIBLIOGRAPHY ........ .. . . . .

VITA .. .... ...... .. .


Page
iv

v



1

6

9

18

28

41

43

47


49

51


i


*


D

D


















LIST OF TABLES


Table Page
I Fluxneter Data .. . .. .. . 21

1I Data for Cross-section Evaluation . . . . 29


















LIST OF PLATES AND FIGURES


Plate Page

I. Photograph of Apparatus, Front View . 10

II. Photograph of Apparatus, Rear View . . 11

Figure

1. Schematic Diagram of Apparatus . . . 12

2. Electrolysis Cell .. . ...... . . 16

3. Fluxmeter Graph . . . . . ...... 22

4. Pressure Dependency Graph . . . . . 24

5. Lid Potential Graph ..... ........... 25

6. Cross-sections as Functions of Ion Energies . . 31

7. Potential Law Graph for Low Energies . . . .36
















CHAPTER I


NEGATIVE IONS


The existence of negative ions was postulated for solutions in

the early days of electrolytic theories of conductance. Consideration

of equilibrium phenomena such as precipitations in solutions has long

demonstrated, as has electrolysis of solutions, the existence of nega-

tively charged particles, other than electrons, in solution. The term

"particles" is used in preference to "ions" due to the presence, in gen-

eral, of solvated clusters in solution rather than simple ions.

Studies of the crystal diffraction of X-rays have also established

that many crystals are ionic in their structure and consist of free ions

held together by electro-static forces. It was later shown that the par-

ticles which carried negative electricity in gaseous discharges were not

restricted to electrons; thus negative ions were shown to exist in the

gaseous state.

As might be expected, certain ions which have been postulated

as organic intermediates have been found by mass spectrometric means

while others have not. In cases where the postulated intermediate is

actually confirmed by mass spectrometric data, its existence may
1









2

generally be regarded as having been established as a free ion. How-

ever, this does not mean that it exists in any other form. A number of

ions, postulated in mechanisms, have been reported by this method;

e. g., O, NOZ, NO3Q(), OH', Li'(2), and Czr(3).

Many of the elements have been shown to have a tendency to

form negative ions, the tendency increasing with increasing electron

affinity. The rare gases are noteworthy in that there are apparently

no stable negative ions formed. This has been attributed to the necessity

for the added electron having a higher quantum number than the outer

atomic electrons, due to the Pauli exclusion principle.

The hydride ion has been the subject of a number of calcula-

tions due to its relative simplicity. It has been shown by Hylleraas (4)

that while the undisturbed state of the atom is not sufficient to produce

stability, the strong interaction in the Is state rearranges the charge

distribution enough to cause stability in the resultant ion. The presence

of this ion in the solar spectrum has now been definitely established (5).

In brief, negative ions are known to exist in all physical

states. They are stable in the solid state due to electro-static equilib-

rium (as in ionic crystals). In the liquid or gaseous state they will

migrate under the influence of applied potentials (as in electrolysis of

solutions). In the gaseous state, they may be produced by such diverse

means as natural processes in the upper atmosphere or, in the laboratory,









3

by thermal dissociation of ionic salts.

The general equations for negative ion production may be

written down:


(1. 1) A+ B" A + B


(1.2) AB + C" = AC + B"


(1.3) A + e + M A + M


(1.4) A2 + e = A" + A


(1.5) A + e = A" + hv


(1.6) A + B" A" + B


(1.7) A + B" AB"*


(1.8) A+ + S = A + S


(1.9) AB + e A" + B+ + e


Equation (1. 1) represents the dissociation of two ions held by electro-

static forces; this process occurs on solution of an ionic salt or upon

the very strong heating of one. Equation (1.2) may be illustrated by the

ion exchange process in solution. In equation (1. 3), M represents any

atom which serves to stabilize the negative ion by removing excess









4

energy. Dissociative attachment by electron collision is represented

by equation (1. 4). Equation (1. 5) is an example of radiative attachment

by an atom of an electron with simultaneous emission of a photon.

(1. 6) is an important equation demonstrating charge exchange between

a negative ion and a neutral atam. This process has been reported by

Dukelskii and Zandberg (6). In equation (1.7) the formation of an ex-

cited negative molecular ion from collision of an atom and a negative

ion is illustrated. Equation (1. 8) represents negative ion formation by

,reflection of a positive ion from a metal surface.

Negative ion destruction may proceed according to one of the

following equations:


(1.10) A" + B = A + B + e


(1.11) A" + B = A + B"


(. 12) A" + B = AB + e


(1.13) A" + S = A + S"


(1.14) A" + B+ AB + h


(1.15) A + B = A* + B*


(1.16) A" ++ B+ M = AB + M









5

(1.17) A + e = A + 2e


(1.18) A' + hy = A + e


(1.19) A" + B* = A + B + e


The symbols, S and M, used in equations (1. 10-1. 19) have the same

meaning as in equations (1. 1-1. 9). In low velocity scattering, the two

most important destructive processes are illustrated by equations

(1. 10) and (1. 11); the first shows electron detachment from a negative

ion by collision with an atom; the second, shows charge exchange

between the ion and the atom.

















CHAPTER II


SCATTERING


Simple scattering theory is based on four assumptions: first,

the system is a conservative one; second, the scattering particle may

be considered initially at rest with respect to the scattered particle;

third, that the force field is a central one; and, a non-essential as-

sumption to simplify the treatment, that the scattering angle is small.

Since the analysis, based on this last assumption, gives results within

the experimental error of an exact treatment (7, 8), it appears to be

a justifiable assumption. The application of this theory to the problem

of this dissertation is given in Chapter V.

Scattering of beams is a powerful tool which has been used for

different purposes in a number of cases. In one of the most simple

experimental forms, it has been used to determine the equivalent wave

length of electrons (9). In recent years, it has been used for such

seemingly diverse purposes as determining the force law between rela-

tively high velocity atoms and molecules (10) and measuring electron

exchange cross-sections (11, 12).









7

Scattering is also applied in determination of nuclear structure,

and has been so used over a wide range of elements. The nucleus to be

studied is bombarded by a particular type of particle (e. g., alpha par-

tides or neutrons) and, through determination of the scattering behavior,

conclusions are drawn as to the structure of the nucleus itself.

The scattering of atoms by gases is similar in principle to the

present work; however, the great difficulties encountered in measuring

the intensities of neutral scattered particles have restricted the measure-

ments to considerably higher energies than those used in the determina-

tion of low velocity ion interaction with gases.

The investigation of elastic scattering of low velocity ions may

be said to originate with the work of Russell, Fontana, and Simons (13)

in 1941. This paper did not make provision for the quantitative separa-

tion of inelastic scattering from elastic scattering, and, consequently,

the results were less definite than later experimental work based on the

apparatus described by Simons, Francis, Fontana, and Jackson (14).

Results obtained in these experiments cover the scattering of H+, H2,*

and H+ ions in a variety of gases. The.potential laws operating over

a given energy range between the ion and the scattering particles have

been evaluated. In many cases the nature of the interaction may be de-

duced from the potential law. Naturally, this technique presents an un-

ambiguous method for determining proton affinities and has been used












for such a purpose (13).

The field of negative ion scattering is one in which little work

has been done (16). With the exception of the negative ion source, the

apparatus used in this dissertation was similar to that used by Simons

and co-workers (8, 12, 14, 15) in the study of positive ion scattering.

Since the low velocity scattering of positive ions in gases has

contributed useful information as to lon-molecule interactions, it was

felt that the same type of experiments with negative ions would also

rield useful results. This view was strengthened by the present lack of

definite knowledge in the field of negative ions. In the light of these

acts, the research for this dissertation was undertaken in order to

contribute to the understanding of the laws governing such behavior.
















CHAPTER III


DESCRIPTION OF APPARATUS


The apparatus used for the scattering measurements was es-

sentially the same as that described by Muschlitz, Bailey and Simons

(16) in Technical report #2 to the Office of Naval Research under con-

tract Nonr 580(01) with several minor changes.

This apparatus utilizes electro-static focusing combined with

magnetic field selection of the desired negative ions. The ions, pro-

duced by collisions of gas molecules with an electron stream, are col-

limated into a well-defined pencil by empirical focusing of electro-

static elements concentric with the desired pencil. The beam then

passes through a magnetic chamber where a particular charge-to-mass

ratio may be selected by varying the magnetic field. The beam is bent

through a ninety degree angle and continues to the final set of electro-

static focusing elements. These elements are, in principle, the same

as the ones before the magnet and are used to refocus the beam which

is tending to diverge as it leaves the magnet chamber. A schematic

drawing of the apparatus is shown in Figure 1, while the exterior is

shown in Plates I and II.


























































Photograph of Apparatus, Rront View




















































Photograph of Apparatus, Rear View
















115v AC


FIG. I NEGATIVE ION APPARATUS
(SCHEMATIC)









13

The beam leaving these final collimating elements is well-de-

fined, of constant charge-to-massratio, and approximately mono-ener-

getic. It is allowed to enter a scattering region containing the scattering

,gaa at some accurately measured low pressure and then passes into a

Faraday cage, C in Figure 1, which collects the transmitted current.

The scattered current is collected on the scattering elements, S and SL.

The scattering elements are a plate, SL, and a cylinder, S,

both of which are concentric with the beam. The plate may be either at

the same potential as the cylinder (and also the Faraday cage) or may

have a small potential applied so as to either remove slow particles

formed by inelastic collisions or to repel all negative particles.

The currents to the scattering cylinder, and collecting cage

are determined by the amplifiers described by Searcy (17). The maxi-

mum full-scale sensitivity is 5 x 10"14 ampere. These currents are

related to the effective cross-sections through the familiar Beer-

Lambert equation expressed in terms of cross-section, path length,

and pressure (see Appendix 1).

Several important modifications in the apparatus have been

made. The filament is now of iridium cataphoretically coated with

thoria (18). Each of three coatings was applied at 30 milliamperes for

15 seconds. Before coating, the ends of the filament were spot-welded.

to 5 mil nickel sheet for support in the filament clamps. The filament









14

emission to the anode is now regulated by a circuit adapted from the

thyratron control portion of a standard ion gauge circuit (19). Finally,

the repeller, R in Figure i, potential has been stabilized using two

voltage regulator tubes (type OA-3) in series.

The thoriated filament was used in preference to the tungsten

previously used in order to obtain a higher ion beam intensity. It has

been found possible to obtain more than ten times the beam intensity

from water vapor at 3 mm. backing pressure (at N in Figure 1) than

from hydrogen gas at 8 mxm. pressure. However, the life of the tungsten

filament in water vapor was reduced to less than the time for an average

run, whereas the thoriated iridium lasted about ten times this long.

The hydride ions produced from water vapor gave the same cross-

sections as those obtained using hydrogen in the ion source.

The water vapor was in dynamic equilibrium with carefully de-

gassed, distilled water maintained at approximately 0* C. by a Dewar

flask containing an ice-water mixture. It was not necessary to maintain

the temperature perfectly constant since small changes in the backing

pressure affect the total current rather than the fractions scattered or

transmitted.

One additional improvement was made. The oscilloscope used

in preceding work was replaced with a General Radio type 1231-3B null-

detector, for locating the null point in the determination of the magnetic









15

field used to bend the hydride beam. The field is determined by balancing

the potential developed by a constant-speed coil placed in the field

against a reference voltage.

Figure Z shows schematically the electrolytic cell, gas train,

and leak system used for producing and introducing the oxygen into the

scattering region. The electrolyte used in the cell was a 5% solution of

barium hydroxide (Baker and Adamson reagent grade). This was chosen

in preference to the potassium hydroxide used in previous work to pre-

vent possible formation of carbon dioxide with the oxygen. Other possi-

ble impurities were presumed to be hydrogen, water. ozone, and hydro-

gen peroxide. To remove these from the oxygen, the gas was passed

through a chain consisting of a platinum filament electrically heated to

redness (to catalyze water formation between the oxygen and any hydro-

gen present), a silver-foil packed tube (to catalyze peroxide and ozone

decomposition), and a phosphorous pentoxide tube (to remove water

vapor present).

The oxygen was then passed into an intermediate pressure region

constructed so that it could be pumped on through either or both of two

capillaries of different lengths. These were connected to a mercury

diffusion pump through a trap cooled by liquid air. From the interme-

diate pressure region, another capillary permitted the oxygen to enter

the scattering region. It was possible with the arrangement used to




























w t
To
To SC.








Fig. 2-Electrolysis Cell









17
-3
obtain equilibrium pressures in the range 0. 5 3. 0 x 10-3 mm of

mercury. This was adequate for the purpose.
















CHAPTER IV


EXPERIMENTAL PROCEDURE


In order to remove residual traces of gas from the apparatus

before scattering measurements were started, the entire apparatus was

evacuated by four high speed mercury diffusion pumps as described by

Muschlitz, Bailey and Simons (16). The pumping was continued until the

pressure was of the order of 2 or 3 x 10-5 mm. of mercury as measured

by the ionization gauge before the measurements began. The coolant

used on the pump traps was liquid air which expedited rapid removal of

condensible gases from the apparatus and prevented mercury vapor from

entering the system. When the pressure reached this value, the ion

source chamber was opened to the water vapor, and the filament and

anode voltages applied. The ion beam was focused to the Faraday cage

by varying the magnetic field and adjusting the focusing elements for

maximum ion intensity.

The method used in the past to determine ion velocity, i. e.

a retarding potential on the final elements (20), was found impractical

in the present apparatus. An energy correction, AV, applied to the

18








19

potential difference between magnet chamber and cathode was determined

in two ways. The first method utilized the mass spectrometer equation:


(4. 1) M HZrZ or, since r is an apparatus
e ZV

constant, and m/e is constant for H",


(4. ) V = kH2. Since V = V + AV, it


follows from (4. Z) that


(4.3) VM kHZ + AV


Thus, plotting the square of the magnetic field needed to focus

the hydride beam for maximum intensity against the potential of the

magnet chamber, as measured in volts, gives a straight line with inter-

cept equal to the velocity correction in volts. The magnetic field is ex-

pressed in arbitrary units.in terms of the reading, D, of a Helipot which

is placed across a known reference potential, E^. D = Em which

is proportional to H. Therefore, the actual plot was based on the rela-

tions


(4.4) V( = k'Em + AV = k'li D2 + AV


Equation (4.4) will give the same intercept as would equation

(4. 3). The different slope is immaterial to the determination of the









2z

energy correction. Table I together with Figure 3, illustrate a plot

of the data as used in this research.

The second method of determining the energy correction was

to measure the total current at a number of voltages in the vicinity of

zero ion energy and extrapolate these voltages to zero total current.

Since the energy resolution at the magnet potential used was 3 e. v.,

the extrapolated voltage was increased to 3 ev. and this value was

averaged with that obtained by the first method to give a value of AV,

This process was then repeated at the end of each run to account for

any changes in conditions. The average of the two values obtained was

taken to correct all points during the run. These values were self-

consistent within 0. 5 e. v. over a twenty hour run.

As a compromise between maximum beam intensity (with an

energy resolution of 6 e. v. ) obtained with the magnet chamber main-

tained at 395 v. positive with respect to the cathode and smaller beam

intensity (with better resolution), the magnet chamber was maintained

at approximately 250 e.v. positive with respect to cathode during the

scattering measurements. This gave the 3 e.v. resolution mentioned

above.

Source conditions were maintained essentially constant during

a given set of data in order to preserve the constancy of the ion energy

in so far as possible.















TA LE I

FLUXMETER DATA



V E
(e. ,v) (arbitrary units)


300 4.16

280 4.00

260 3.82

240 3.63

220 3.44

200 3.24

180 3.02

160 2.78

140 2.52

47.09 0.00*


* Method of least squares.























































Fig. 3--Fluxmeter Graph









23

To investigate the possibility of multiple scattering in the pres-

sure range covered,; data for RO/RS were plotted as a function of

T P
10 RO
10 1 s -3- !
RT


This plot is given in Figure 4.. The linearity of the plot shows agS/a.

to be pressure independent in the pressure range 0 3 x 10'3 mm.,

One important change in technique used in this experiment was

the evaluation of the RT ratios at a negative lid potential. This potential

was -4 v. for higher energies than 50 v. and -2 v. for lower energies.

That this is justified may be seen by referring to Figure 5 in which

R/RS is plotted as a function of the lid potential. Below -1 v.: the

ratio is seen to become essentially constant. Since the negative potential

prevents slow negatively charged particles from reaching the lid, this

ratio is very nearly equal to R/RT.. The total ratios taken in this

fashion are probably more accurate than those obtained by the more labo-

rious method used in the past. This was to connect the lid, SL,. to the

scattering cylinder, and measure the current to the two while they were

maintained at amplifier ground potential. Under these conditions it is

possible that slow particles produced in the defining cylinder will be

measured on SL. The present method enables the elastic cross-section

to be obtained under the same experimental conditions, except for this















0aTP/F1
10 -1
.o __ 0. 00




1.50









0
S
RS

1.25













1.00 _
Fig. 4-- Pressure Dependency Graph







SL


Fig. S-Idd Potential Graph


1.50


0

RS30






1.30









26

lid potential, as the total cross-section. Therefore, it offers largc

advantages over the prior nmettod, as re~ardE. accuracy and convenience

of measuring.

A firat-ordcr correction factor was applied to the R /R(

data. in view of the constancy of the slope at high positive potentials in

Figure 5. This was the extrapolation of the experimental ratios to zero

lid potential to account for loss in the beam due to the defocusing action

exerted by this potential on the elastically scattered ions. The action of

this correction was to increase the value of the elastic cross-section by

about 10 per cent. The extrapolation was carried out on the assumption

that the slope of the linear portion of the curve was independent of the

ion energy. This was found approximately true by experiment, The

same behavior of RO/Rg has been observed for the previous work on

the scattering of hydride ions in hydrogen (16). It is therefore reason-

ably certain that this is an apparatus effect rather than a physical phe-

nomenon.

The method followed in taking the current ratios was to admit

the oxygen to the scattering cylinder and to allow the pressure to equi-

librate before slowly filling the McLeod gauge. The pressure measure-

ments have been estimated to be accurate to t 1, 073 in the range

measured. After equilibrium was established, from three to eleven

ratios were taken at each energy. The average value of these reading









27

was taken as the "R" value for that energy. The oxygen was then shut

off from the scattering region and, after establishing equilibrium,

readings were taken for the "empty tube" or i"RO" values at the lowest

apparatus pressure attainable.

The pressure measurements were obtained in a carefully

calibrated McLeod gauge of 500 ml. capacity in the following way:

the average capillary correction for the pressure range employed was

determined as an average of from three to twelve readings; this value

was then subtracted from the scattering pressure reading which was

obtained in the same fashion. The capillary correction was taken at

the same pressure as the "empty tube" ratios. The scattering pres-

sure measurement was made each time gas was admitted to the scat-

tering tube. All measurements of cross-sections were made in the

vicinity of 1. 4 x 10-3 mm. of mercury. This pressure gave ratios

which were in the optimum range of 0. 6 0. 8, i. e. about 30 per cent

of the beam scattered. If more than 60 per cent of the beam is scat-

tered multiple collisions will seriously affect the results.

When shutting down, the system was pumped to a pressure of

the order of 5 x 106 mm. of mercury by the diffusion pumps. The

pumps were then shutdown and the system slowly filled with nitrogen

to one atmosphere pressure.

















CHAPTER V


TREATMENT OF DATA


The results listed in Table 2 for the scattering investigated

in this research show the interaction cross-section of the hydride ion

and oxygen gas for three types of scattering. The data contained in this

table are plotted in Figure 6 over the energy region investigated. The

top curve shows the variation of the total cross-section with energy;

the center one, that of the elastic cross-section; and the lowest one,

the difference which is equated to the inelastic cross-section as dis-

cussed in Appendix I.


Analysis of Data for Elastic Scattering

This analysis is based on the four classical assumptions men-

tioned in Chapter II. The first of these, that interaction is attributable

to a central force field, is expressed as an attractive inverse n'th

power law of the particle distance.


(5.1) V = .K
rn







TABLE II

DATA FOR CROSS-SECTION EVALUATION


0 0 Pc x 103 aT as
V(e.v.) AV(e.v.) RS RS RT RT T C VSLe. v.) (mm. Hg) (cm2/cm3) (m2 /cm3
S5 (mm. Hg) (cm /cm ) (cm /cm )


139.9

118.8

99.9

79.9

64. 9

49.9

43.8

33. 8

30.2

23.8

22. 2

20.2


48.1

47.2

48.1

48. I

48.

48. 1

47.2

47.2

46 .8

47.2

46.8

46.8


0.977

0.980

0.986

0.988

0.988

0.984

0.985

0.988

0.992

0.988

0.995

0.993


0.736

0.734

0.738

0.744

0.751

0.756

0. 759

0.770

0. 786

0.779

0.788

0.792


0.998

0.997

0.998

0.998

0.999

0 998

0.998

0.997

0.998

0.997

0.997

0.997


0.623

0.623

0.624

0.631

0.643

0. 660

0.660

0.678

0. 692

0.691

0.704

0.707


28.0

24.9

27.8

27. 8

28.9

28.9

Z4. 9

25.0

27.8

25 .0

27. 0

27.0


23. 0

21.0

19.0

17.0

15.5

14.0

13.8

11.8

11.1

9.9

9.5

9. 1


1.378

1.431

1.391

1.391

1.370

1. 370

1.43L

1.443

1.372

1. 443

1.391

1 391


101

102

10o

97.4

95.6

89. 8

84. 9

78 .5

79 .0

74. 2

73. 9

73.0


60.1

57. 2

61.2

58. 7

58.0

55.8

52. 1

49.5

49.4

47.6

48.8

47.2








TABLE II--Continued


0 0 Pc xO 104 M as
V(e.v.) AV(e. v. RS R) RT R T* C VSL,(e.) (cm 1m3)
s s_(rnm. Hg) (cm /cra3 (cm /erm3)


17.2

13.8

11.8

9.8

7.8

5.8

5.2

3.2


46.8

47.2

47. 2

47.2

47.2

47. 2

46. 8

46. 8


0.994

0.988

0.987

0.989

0.985

0.984

0,984

0,975


0.789

0.777

0.773

0.768

0.757

0.757

0. 756

0.731


0.997

0.994

0.989

0.988

0.986

0.982

0.994

0.979


0.703

0,686

0.678

0.668

0.660

0.646

0. 655

0. 634


27 .8

24.9

25.0

25. 0

25.1

25.1

26,.9

26,8


8.5

7.9

7.5

7.1

6.7

6. 3

6. 1

5.7


1, 372

1.373

1.385

1.389

1,387

1,387

1,410

1.412


75.4

79.2

80. 2

82. 8

84.9

88.6

86.8

90.8


48.8-

49. 6

50.0

51.2

53.2

52.4

51,9

56.9


- --












Voltage


100


125









32

The second assumption is that the oxygen molecule is initially at rest

with respect to the hydride ion. Since one has thermal energy and the

other has energy of at least several volts, this is certainly valid. The

third assumption is that the system is conservative. This assumption

is probably true at low energies, but becomes less safe at higher ener-

gies. As previously stated, the simplifying assumption is made that

the scattering angle is small. This assumption is certainly not true for

those ions which were scattered as they were about to leave the scatter-

ing cylinder; however, most of the scattering occurs in the upper half

of the scattering cylinder since the beam intensity drops in an exponen-

tial fashion. It has been shown by Kells ( 7) that a treatment of scattering

data based on the assumption that the cosecant of the relative scattering

angle equals the cotangent of that angle gives results which agree within

one per cent of an exact treatment described by Simons, Muschlitz,

and Unger (8 ).

For the system hydride ion oxygen molecule, the hydride ion

may be considered as having an initial velocity v0 and mass ml; while

the oxygen molecule will be treated as a single particle of mass m2,

initially at rest.

The distance between the particles is defined as r, with the

distance of closest approach defined as r0. The relative scattering

angle referred to the molecule is taken as .












Since the sys-icn io a conservative one, defining as the

relative radial angle,


(5.2) / rA = vob = a conasant, where / is the re-

duced mass and b is the impact parameter. The rclativc total

energy of the system is

(5.3) E M

Substitution of (5.1) givec

(5.4) Er A (i2 + r2Z*) & K I _v
a ran 0


Stice r = 0 when r = r equation (5.4) may be solved for

the irnpact parameter, b,

(. z 2 2.n
(5) b = r + r, and, averaging over the
E

scattering length, "I",


r. dx + 1 r dx
(5. 6) bas .o













= ~~" r" dx


K 2 Z-n
+ --,1 r dx .
Jo 0


Since a = NTba
S a

r"l" r"l"
(5.7) a N T + rN-+E / r2-n
"ro 0 E"o1" 0 d


Relating the minimum absolute scattering angle,

-1
S= tan a where a is the radius of the scattering cylinder
II" x

hole, to the relative energy, E,


(5.8) tane =


1
KrZ r (n/2 + 1/z)
Er, r(n/2)


KC
- -Tr-(8) and (7)
zo


applying the assumption of small angle scattering to the equation

relating the relative and absolute scattering angles


(5.9) coto = cot


+ L cSc lWC cot 8
m2 A


The measured ion energy is W = 1/2 mlv0

Equation (5. 7) now becomes

2/n
(5,. 10) a, S V = NC
Sn +2 aW

+ Nr a2n nm (:n1"C)(2/n) ( 12 /n
Z/. \Wal










from which

(5.11) a WZ/ = Q NnKC"" I a
I=\n+r
S a ( 2 ""*

Upon taking logarithms of the first equation (5. 11),

(5. 12) log Q + 2/n log W = log Q follows.
S

This last equation shows that a plot of the logarithm of mS

against the logarithm of the ion velocity should be a straight line with

slope of *Z/n and intercept of the logarithm of Q. The intercept, log Q,

is used in evaluating the constant of the potential law from equation

(5. 11). It should be stressed that this law will hold only for the region

where all assumptions are valid. A plot of (5. 12) for hydride ions in

ogygen from 3420 volts is given in Figure 7. From this plot, the

slope was found to be -0.072 and the intercept, 1. 79. By utilizing the

preceding equations, the potential function for this range

(ba = 2.0 2.3 A ) has been evaluated as

(5.13) V - 10 2Z2 with r expressed in centi-
r28

meters, and V in electron volts,

The previous work on the scattering of low velocity hydride

ions was in hydrogen; in which, there is no tendency for compound

formation. The H" -- H2 interaction appeared to follow an ion-dipole



















() cm ocr 141 n


O


~ 0 0


I 4


1.80





1.70





1.60

log oS



1.50






1.40





1.30





1.20


.1 4


4 4


Fig. 7--Potential Law Graph at Low Energies


4 4


10


n0 q


1)cr W


1 -nn









37

(n = 4) type of attraction at low energies. The high value of the ex-

ponent in the potential law observed for oxygen at these low energies

is attributed to a short range attractive force arising from a valence

(or exchange) interaction between H"'and OZ. It would seem that the

data indicate IHOz to be a stable structure. This ion has been known to

exist in solution for some years as the anion of hydrogen peroxide (20).

The minimum in the elastic curve may be a typical property of

negative ion scattering since it has now appeared in both cases investi-

gated. For the hydride-hydrogen case, the minimum appeared at

about 55 volts and showed a gradual rise thereafter. In the present

case, as is shown in Figure 6, the minimum occurred at about 20

volts ion-energy and the cross-section then showed a gradual rise to

about 100 volts. Since this minimum was found at an ion energy of

twenty volts, it is quite possible that excitation of the oxygen molecule

takes place at higher energies. An excited electronic state, 'Ag,

having an energy of about 1 e. v. above the ground state is known for ox-

ygen (21). It would appear that this is a probable explanation of the

rise in the cross-section at higher energies. Such an excitation would

appear in the elastic measurement since the inelastically scattered ion

will still retain considerable kinetic energy.

The excitation postulated in the case of the hydride ion hydro-

gen molecule scattering (16) involves the excitation of the molecule to









38

the 1 u state. As this lies about 11 e.v. above the ground state of

hydrogen, the maximum probability for this excitation should occur at a

higher ion energy than should the excitation of oxygen postulated in the

present research. Comparison of the present data with those obtained

in the scattering in hydrogen bears out this theory. The elastic cross-

section for the hydride hydrogen system is still increasing at 400 e. v.

ion energy.

A search for positive ion formation was made at 400 e. v. ion

energy by measuring the current to the scattering lid when various neg-

ative potentials were applied to the lid. Since the ionization potential

of oxygen is 12. 5 e. v., no detectable ionization was anticipated at this

energy and no current was measured to the lid.

The inelastic cross-section curve qualitatively resembles that

obtained in the hydrogen scattering data above twenty volts. In the light

of the conclusions reached in that experiment, and also those obtained

by Hasted (11), it seems reasonable to conclude that the process taking

place above twenty volts is principally "ionization" of the hydride ion

according to the general type of equation (1. 10).

The inelastic cross-section for the system H -- H2 tended to

approach zero at lower energies. A similar behavior was noted by

Hasted (11) for the inelastic scattering of H" in the rare gases. In the

present research, the inelastic cross-section appears to rise below









39

twenty volts ion energy. Because of the rise in cross-section at lower

energies and because of the low absolute value of AE for the exchange

process, it seems reasonable to assume that the primary process which

is taking place in this neighborhood is the charge exchange phenomenon,

(6.1) H- f+ = H + 02 + aE.

AE is the energy difference between the electron-affinity of atomic

hydrogen and that of molecular oxygen. The probability of such a process

increases with a decrease in the absolute value of 4E. Values for the

electron affinity of molecular oxygen vary, but, assuming an approxi-

mate value of 0. 9 e. v. and using 0. 75 e. v. for the electron affinity of

the hydrogen atom there is obtained an absolute value of 0.15 e.v. for

the energy difference.

An estimate of the probable error in the determination of the

potential law, equation (5. 13), may be made assuming 0. 5% error in
o 0
RT/RT and RS/AS, 1% error in the pressure measurements, and

I 1 e. v. uncertainty in the ion energy. The probable errors in 0T,

aS and av are 1.5%, 4%, and 8% respectively. The resulting

probable error in the exponent, n, is L7. It is difficult to make an

estimate of the error due to the influence of inelastic scattering on

the elastic cross-section. This will be appreciable at ion energies

above 20 e.v. At very low ion energies the assumption that the










40

initial momentum of the oxygen molecule is negligible is questionable.

It is felt, however, that the overall uncertainty in the exponent is not

much more than 10.















CHAPTER VII


CONCLUSIONS


Investigations have been made of the scattering cross-sections

of hydride ions in gaseous molecular oxygen in the energy range of three

volts to one-hundred-and-sixty volts incident ion energy. The cross-

sections for both the elastic and inelastic types of collision were investi-

gated and the results point to the following conclusions.

In light of the elastic scattering results, it seems quite reason-

able to assume that in the low energy region there is a tendency for

formation of the OaH ion, The potential expression which best fits

the data is


1220
(7.1) V = 10
r28
o
over the range of interaction 2. 0 2. 3 A. It is possible that this type

of behavior is a general one for negative ion collisions in which

valence or exchange forces are involved. Above twenty volts, the inter-

pretation is complicated due to a rise in cross-section which is attri-

buted to excitation of the molecular oxygen at the expense of kinetic

energy from the ionic beam.









42

The inelastic cross-section goes through a much sharper mini-

mum in the same region as the elastic scattering minimum. The lower

energy cross-sections are attributed to charge exchange between the ion

and the molecule while the higher energy cross-sections are primarily

the result of simple detachment of the electron from the ion to form a

hydrogen atom.















APPENDIX I


(1) I Io exp (-* cr p) whore X is the current at dis-
tance x along the scattering path compared to Q, the current at the

start of the scattering paths crT ia the total cross-section for the

interaction (which may be attractive or repulsive); and p is the pres-

sure of scattering gas. Since all collisions are either elastic or inelas-

tic the total cross-section may be equated to the sum of the elastic and

inelastic cross-sections. Differentiation of (1) gives


(2) -dlx = dLT a Ix O pdx which, together with additivity

of the cross-sections, gives rise to


(3) -dk d( a td a gpdx and


(4) *dl1 a f(a Updx.


Division of (3) by (2) results in

d Ix( a) as



Integrating over the scattering length and indicating the total scattered

current by IT and the elastically scattered current by Ig, gives
43









44


(6) E = a Similarly, 1,= a where
T T T T

II is the inelastically scattered current.

Due to the design of the scattering region, all particles which

are not sufficiently deflected from the beam path will go to the Faraday

collecting cage and be counted as transmitted current. Essentially all

other ions will be collected on either the scattering cylinder or the lid

of the cylinder. The currents to the-collecting cage, the scattering

cylinder and the lid of the scattering cylinder may be represented by

IC, IS- ISL, respectively when the total ratios are being taken. When

the retarding potential is applied to the lid, IS and ISL become

Is' and LL'.

Since it is far simpler to work with fractions of the total cur-

rent than it is to calculate absolute currents as indicated by a potential

drop across a high resistance, it is found convenient to define the

following fractions:

Ic Ic
(7) a) RT = =
IS + Ic + sL I C+ IT


b) Rg IC IC
S+ IC I + IE

RIc IC
c) RI = C 'C
ISL +C c C c +








15

Equations (7) may be: rearranged to give

S1 S L 1T
(8) a) ___ s
RT IC IC


b) 1
RS

I
1
c) 1
RI


S -IE
I C IC



IC C


In light of equations (6),
-1 I
(9) s -.---- aT and aI = .R. .
RT RT

Rearrangement of (1) gives, with the length "1",


In L = pa "1"
IC


therefore


(10) a In 0 1 In -L
P'"1" IC P11" RT

The actual equation used, however, was one based on scattering at two

different pressures; to account for small errors in alignment, beam

spread due to space charge effects. One of these pressures was the

lowest vacuum pressure obtainable and gave a scattering ratio, RO

very close to one. The corrected equatiir becarne'











RO
(11) =_________. In
T (273. 2 K) "1" (P P) RT


= F log ; where
P P0 RT


S T(Z. 303)
273. 2*K "1


This same correction is applied to the RS values; i. e. R

ratios which were close to unity were used to obtain aS. Since

aI- a T ag it is not essential to measure I1L separately in

order to evaluate a
















APPENDIX II

Definition of Symbols


Figure 1


A

C (Ion Source)

C (Scattering
Elements)

D

EC


M
FE




N

1', R2,

S
SL


Anode

Cathode

Collecting Cylinder or Faraday Cage

Defining Cylinder

Electron Collector

Focusing Elements

Magnet Chamber

Meters

Nozzle

Electron Repelling Elements

Scattering Cylinder

Scattering Cylinder Lid or Plate













Text

aT
aS

al


b




H

1

p
P
r (p.

r (p.

ES,


19)
32-34)
o


RT, RTB

ro

VSL
V (pp. 28-41)

V (p. 19)


Total Cross-Section in cm-1

Elastic Scattering Cross-Section in
cm-1

Inelastic Scattering Cross-Section in
cm-1
Impact Parameter
Relative Ion Energy in e.v.

Scattering Function (See p. 46)
Magnetic Field Strength
Length of Scattering Region

Scattering Pressure in mm of g

Radius of Curvature
Ion-Molecule Distance
Scattering Ion Current Ratios
(see pp. 44-46)
Total Ion Current Ratios (See pp. 44-46)

Distance of Closest Approach between
Ion and Molecule
Scattering Cylinder Lid Voltage
Ion-Molecule Interaction Potential
in ev.
Ion Energy in Magnet Chamber in e.v.

Ion Energy in Scattering Region in e.v.
















BIBLIOGRAPHY


L. Ttxen, Z. Phys. 103, 463, (1936)

2. Sloan and Love, Nature, London, 159, 302, (1947)

3, Bailey, McGuire, and Muschlitz, in press, J. Chem. Phys,

4. Hylleraas, Z, Phys. 60, 624, (1930)

5. Massey, "Negative Ions, The Cambridge University Press,

Cambridge, 1950, pp. 122-128

6, Dukelskii and Zandberg, Doklady Akad. Nauk S. So S. R 82, 33,

(1952)

7. Kells, J. Chem. Phys. 16, 1174, (1948)

8; Simons, Muschlitz, and Unger, J. Chem. Phys. 11, 322,

(1943)

94 Davisson and Germer, Phys. Rev,, 30, 705, (1927)

104 Amdur and Pearlman, J. Chem. Phys. 8, 7, (1940)

11. Hasted, Proc. Roy. Soc., A205, 421, (1951); A222, 74, (1954)

12. Muschlitz and Simons, J. Phys. Chem, 56, 837, (1952)

13. Russell, Fontana, and Simons, J. Chem. Phys., 9, 381, (1941)

14. Simons, Francis, Fontana, and Jackson, Rev. Scl. Instruments

13, 419, (1942)









50

15. Simons and Cramer, J. Chem. Phys., 18, 473, (1950)

16. Muschlitz, Bailey, and Simons, "Technical Report Number Two

to the Office of Naval Research under contract 580(01)," 1955

17. Searcy, "A Study of Electronic Methods for the Measurement of

Small Direct Currents," M. S. E. Thesis, University of

Florida, 1953

18, Randolph, "A Study of Cataphoretically Coated Cathodes, "

M. S. E. Thesis, University of Florida, 1954

19. Nelson and Wing, Rev. Sci. Instruments, 20, 541 (1949)

20. Joyner, Z, anorg. Chem., 77, 103, (1912)

21. Herzberg, "Spectra of Diatomic Molecules, D. Van Nostrand

Co., Inc., New York, 1950- p. 446

22. Hasted, Proc. Roy. Soc., A212, 235, (1952)

23. Evans and Uri, Trans. Faraday Soc., 45, 217, (1949)

24. Kazarnovski, C. IR Acad. Sci. UR.. S., 59, 67, (1948)

25. Massey, op. cit., p. 28

















VITA


John Murray McGuire was born in New Bedford, Massachu-

setts, on 15 May, 1929. He is the son of Mary Murray McGuire and the

late Thomas Christopher McGuire, Jr. He graduated from Belmont

Abbey Preparatory, Belmont, North Carolina, as Valedictorian in

1945. He then entered the University of Miami, Coral Gables, Florida,

from which he received the Bachelor of Sciencce degree cum laude in

1948 and the Master of Science in 1951. He then entered the Graduate

School of the University of Florida, Gainesville, Florida.










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 ap-

proved as partial fulfilment of the requirements for the degree of

Doctor of Philosophy.


January 29, 1955


Dean, College 6f Arts and Sciences



Dean, Graduate School


SUPERVISORY COMMITTEE



Chairman



A 1-44/ ?

? / x j6. I
/Y: c< ^,^*c <-










Internet Distribution Consent Agreement


In reference to the following dissertation:

AUTHOR: McGuire, John
TITLE: Scattering of hydride ions in oxygen gas. (record number: 559221)
PUBLICATION DATE: 1955


I, joA/6 Q /I (1 /re as copyright holder for the
aforementioned dissertation, hereby grant specific and limited archive and distribution rights to
the Board of Trustees of the University of Florida and its agents. I authorize the University of
Florida to digitize and distribute the dissertation described above for nonprofit, educational
purposes via the Internet or successive technologies.

This is a non-exclusive grant of permissions for specific off-line and on-line uses for an
indefinite term. Off-line uses shall be limited to those specifically allowed by "Fair Use" as
prescribed by the terms of United States copyright legislation (cf, Title 17, U.S. Code) as well as
to the maintenance and preservation of a digital archive copy. Digitization allows the University
of Florida or its scanning vendor to generate image- and text-based versions as appropriate and
to provide and enhance access using search software.

This/nt flpe missions pro ibits use of the digitized versions for commercial use or profit.


S atre oCopyright I-lder


Printed or Typed Name of Copyright Holder/Licensef


Personal information blurred




Dat of Sinature

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




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs