Mass Spectrometry in Inorganic Chemistry

13 Mass Spectrometry of Phosphorus Hydrides T. P. FEHLNER and R. B. CALLEN Department of Chemistry and Radiation Laboratory, University of Notre D a m e , Notre D a m e , I n d .

Downloaded by CORNELL UNIV on May 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch013

Appearance

potentials,

abundances diphosphine-2, using

heats

of the principal and

of

diphosphine-4

a mass spectrometer

with

value for the heat of formation diphosphine-2

has been calculated

that in conventional obscures

the

formation,

positive

ion sources

mass spectrometry

and

ions from have

been

collision-free of 26

relative phosphine, determined

sampling.

±8 kcal./mole

A for

from the data. It is shown decomposition of

completely

diphosphine-4.

A s t h e source of a mass spectrometer operates at e l e v a t e d t e m p e r a t u r e s , t h e mass spectrometry—i.e.,

relative abundances

and

appearance

potentials of t h e p r i n c i p a l ions p r o d u c e d b y e l e c t r o n i m p a c t — o f t h e r m a l l y u n s t a b l e substances c a n b e o b s c u r e d b y d e c o m p o s i t i o n o c c u r r i n g i n t h e i o n source.

D i p h o s p h i n e - 4 is a c o m p o u n d that decomposes r a p i d l y at

r o o m t e m p e r a t u r e . I n o r d e r to o b t a i n u n a m b i g u o u s i n f o r m a t i o n , some m e t h o d of c o l l i s i o n - f r e e s a m p l i n g m u s t b e u s e d ( 5 ) .

T h e results are

i n t e r e s t i n g since i t appears that t h e mass s p e c t r o m e t r y of p u r e d i p h o s p h i n e - 4 has not b e e n p r e v i o u s l y o b s e r v e d . Experimental T h e mass spectrometer a n d s a m p l i n g system u s e d here are b a s i c a l l y s i m i l a r to i n s t r u m e n t s p r e v i o u s l y d e s c r i b e d (4, 5, 16), a n d o n l y a b r i e f c h a r a c t e r i z a t i o n is g i v e n b e l o w . T h e s a m p l i n g system is i l l u s t r a t e d i n F i g u r e 1. T h e gas or m i x t u r e of gases to b e e x a m i n e d flows f r o m a c o l d reservoir t h r o u g h the center t u b e of the q u a r t z flow reactor, w h o s e t e m p e r a t u r e m a y b e v a r i e d f r o m r o o m t e m p e r a t u r e to a b o u t 800°K. T h e center p o r t i o n of t h e efflux of t h e reactor is s a m p l e d b y means of a c i r c u l a r orifice l e a d i n g i n t o a s e p a r a t e l y p u m p e d c h a m b e r . T h e pressure o n t h e h i g h s i d e of t h e l e a k is k e p t b e l o w t h e v a l u e w h e r e the m e a n free p a t h is c o m p a r a b l e to t h e orifice d i m e n s i o n s . T h e b e a m is c o l l i m a t e d a n d t h e n i o n i z e d i n a s e p a r a t e l y p u m p e d mass spectrometer c h a m b e r . T h e t o t a l b e a m l e n g t h is 181

Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

182

MASS

S P E C T R O M E T R Y

I N

INORGANIC

C H E M I S T R Y

3.1 c m . T o i n t r o d u c e d i s c r i m i n a t i o n against b a c k g r o u n d a n d other source effects, the n e u t r a l b e a m is m o d u l a t e d i n the second c h a m b e r at 590 c.p.s., u s i n g a v i b r a t i n g r e e d d r i v e n b y a n a u d i o oscillator. T h e t o t a l o u t p u t of t h e mass spectrometer, w h i c h is a n o r m a l c i r c l e , 9 0 ° , 8.75 c m . r a d i u s of c u r v a t u r e , m a g n e t i c sector m a c h i n e h a v i n g a q u a d r u p o l e i o n lens, a n d u s i n g e l e c t r o n m u l t i p l i e r d e t e c t i o n , is f e d i n t o a n a r r o w - b a n d a m p l i f i e r l o c k e d - i n to the f r e q u e n c y a n d phase of the c h o p p e r . B y e m p l o y i n g a m o d u l a t e d b e a m system, a n y u n m o d u l a t e d signals a r i s i n g f r o m b a c k g r o u n d gas, r e s i d u a l b e a m m o l e c u l e s ( m o l e c u l e s w h i c h enter the source as b e a m m o l e c u l e s a n d are i o n i z e d after b e i n g scattered a n d b e f o r e b e i n g p u m p e d a w a y ) p y r o l y s i s p r o d u c t s , etc. are e l i m i n a t e d a l t h o u g h t h e y s t i l l c o m p e t e w i t h the m o d u l a t e d s i g n a l as noise.


Shutter

Pump 40

l/«

Figure 1.

Pump

Pump 115

l/

s

50

•/sec

Schematic drawing of sampling system

T h e r e are three other effects w h i c h c a n result i n signals coherent w i t h the b e a m s i g n a l (4). L a r g e pressure fluctuations i n the source c a n h a v e s u b s t a n t i a l c o m p o n e n t s at the c h o p p i n g f r e q u e n c y . T h e s e are m i n i m i z e d b y u s i n g a d i f f e r e n t i a l l y p u m p e d b e a m c o l l i m a t i o n system. H o w ever, w i t h the d i f f e r e n t i a l l y p u m p e d system there is a net flow b e t w e e n the different c h a m b e r s . P a r t of this flow w i l l c o i n c i d e w i t h the b e a m , w i l l b e c h o p p e d , a n d w i l l b e i n d i s t i n g u i s h a b l e f r o m the b e a m . A s o l e n o i d o p e r a t e d shutter, w h i c h b l o c k s the b e a m b u t does not affect the flow, a l l o w s this extraneous s i g n a l to b e d e t e r m i n e d . W i t h n i t r o g e n as a test gas this s i g n a l w a s o n l y 3 % of the t o t a l m o d u l a t e d s i g n a l i n this a p p a ratus. F i n a l l y , w h e n the n e u t r a l b e a m is i n t r o d u c e d i n t o the i o n i z a t i o n c h a m b e r , a d e n s i t y of r e s i d u a l molecules is b u i l t u p o w i n g to the finite p u m p i n g s p e e d at the source exits. I n the present a p p a r a t u s t h e d e n s i t y of these r e s i d u a l m o l e c u l e s is a b o u t 0.1 times the d e n s i t y of b e a m m o l e cules at the steady state for n i t r o g e n gas e v e n t h o u g h a r a t h e r o p e n source c o n s t r u c t i o n w a s e m p l o y e d . W h e n the b e a m is m o d u l a t e d , t h e r e is a t e n d e n c y for the r e s i d u a l gas d e n s i t y to f o l l o w the b e a m d e n s i t y


13.

FEHLNER AND CALLEN

Phosphorus

183

Hydrides

changes. T h i s effect is not i m p o r t a n t p r o v i d e d the m o d u l a t i o n p e r i o d is short w i t h respect to the t i m e constant of the v a c u u m system (4, 5). H e r e a m o d u l a t i o n p e r i o d of 1.7 msec, a n d a v a c u u m t i m e constant of 50 msec, gave a n i n p h a s e c o m p o n e n t of the t o t a l pressure v a r i a t i o n of 3 Χ 10" . W i t h this system the i o n s i g n a l o b s e r v e d is a t t r i b u t e d to gas i n t r o d u c e d i n t o the source i n a n essentially collision-free m a n n e r . T h i s c o n trasts w i t h c o n v e n t i o n a l s a m p l i n g w h e r e gas is s i m p l y l e a k e d i n t o t h e source a n d suffers m a n y collisions w i t h the hot w a l l s of the source before b e i n g i o n i z e d or p u m p e d a w a y . 5


Appearance

'Potentials

A p p e a r a n c e potentials of the p a r e n t ions of p h o s p h i n e a n d d i p h o s p h i n e - 4 w e r e d e t e r m i n e d u s i n g a m o d e l 12-107 B e n d i x time-of-flight mass spectrometer, w h i c h w a s p r e v i o u s l y m o d i f i e d for r e t a r d i n g p o t e n t i a l d i f ference (RPD)

a p p e a r a n c e p o t e n t i a l measurements

Xenon and

(6, 10).

k r y p t o n w e r e u s e d as c a l i b r a t i n g gases, a n d the i o n i z a t i o n potentials, d e t e r m i n e d for b o t h the p r o t o n a t e d a n d d e u t e r a t e d m o l e c u l e s , w e r e i d e n t i c a l w i t h i n e x p e r i m e n t a l error.

Results b y the RPD

compared

by

with

those

obtained

photoionization

method since

can

be

a value

of

10.18 e. v. w a s o b t a i n e d here f o r the i o n i z a t i o n p o t e n t i a l of N H ; this is 3

i n g o o d agreement w i t h the p h o t o i o n i z a t i o n v a l u e of 10.154 e. v.

(18).

A p p e a r a n c e potentials of the f r a g m e n t ions w e r e d e t e r m i n e d o n t h e mass spectrometer u s i n g m o l e c u l a r b e a m s a m p l i n g u s i n g a s e m i l o g t e c h nique (5).

T h e p a r e n t i o n w a s u s e d to c a l i b r a t e the voltage scale.

P H / ions f r o m P H 2

4

The

w e r e a n e x c e p t i o n to this since the v a n i s h i n g c u r r e n t

m e t h o d ( 8 ) was u s e d b e c a u s e of the l o w i n t e n s i t y of these ions a n d the presence of s m a l l P H

3

i m p u r i t i e s . T h e stated error i n t h e

potentials is a n estimate b a s e d o n the p r e c i s i o n of e a c h

appearance

measurement,

the n u m b e r of d e t e r m i n a t i o n s , a n d the m e t h o d u s e d to d e t e r m i n e t h e value. I n o r d e r to c a l c u l a t e the i o n i c heats of f o r m a t i o n , the process for f o r m i n g the i o n m u s t b e k n o w n . D e t e r m i n i n g the correct process is not easy; h o w e v e r , a p p e a r a n c e potentials c a n g e n e r a l l y be e s t i m a t e d , a n d the most p r o b a b l e process c a n b e chosen b y c o m p a r i s o n w i t h the e x p e r i m e n t a l values.

B y a s s u m i n g that the a p p e a r a n c e

potential measured

refers to the i o n f o r m e d i n its g r o u n d state w i t h no excess energy, the heat of f o r m a t i o n c a n b e c a l c u l a t e d

(9).

Phosphine P h o s p h i n e w a s p r e p a r e d as d e s c r i b e d p r e v i o u s l y ( 1 ). T h e results of this s t u d y a l o n g w i t h those of the p r e v i o u s studies ( 3 , 11, 13,15,17) g i v e n i n T a b l e I.

A

(P /PH )—i.e., +

3

the a p p e a r a n c e

p o t e n t i a l of


are P

+

184

MASS S P E C T R O M E T R Y I N INORGANIC C H E M I S T R Y

Table I.

Relative Abundances and Appearance Potentials of the Refotive m/e

This work (50 e. υ.)

34 33 32 31

61 30 100 35

Diphosphine-2

64 63 62

70 60 100

Diphosphine-4

66 65 64 63 62 34 33 32 31

100 8 52 46 60 1 max/ 3' 8' 8'


Phosphine

abundance Others (70 e. V.)

75.2 21.8 100.0 24.1

e

α e e

85.0* 27.6 * 100.0* 26.4 d

68.0 25.4 100.0 40.2

e e e e

100 16» 69 67 1190* (5) ev 2 14

100 12 68 59 77 70 28" 134" 88

b

α

e

6

e

b

e

e

b

e

b

6

a

"See (17). See (14). See (15). See (11). b

c

d

f r o m P H , is s o m e w h a t d o u b t f u l since t h e i o n efficiency c u r v e e x h i b i t e d 3

considerable tailing. For

this m o l e c u l e

the spectrum

obtained

on the machine

collision-free s a m p l i n g w a s n e a r l y i d e n t i c a l to t h a t o b t a i n e d w i t h ventional sampling.

with con

W i t h i n e x p e r i m e n t a l error, t w o o f t h e i o n i z a t i o n

potentials p r e v i o u s l y m e a s u r e d

agree

(11, 17)

w i t h t h e RPD

value

r e p o r t e d here. From A ( P H

2

+

/ P H ) a n d t h e i o n i z a t i o n p o t e n t i a l o f P H o n e notes

that D ( H P — H ) = 2

3

3

3.2 e. v . i n t h e P H

3

+

ion. B y assuming that the

average P H b o n d energy, Ε ( Ρ — Η ) , i n t h e ions is 3.2 e. v., a p p e a r a n c e potentials of t h e f r a g m e n t ions c a n b e e s t i m a t e d f o r v a r i o u s processes. T h e results g i v e n i n T a b l e I I f o r t h e most p r o b a b l e process a r e consistent w i t h t h e m e a s u r e d a p p e a r a n c e potentials. F o r P a n a l t e r n a t i v e v a l u e of +

15.9 is o b t a i n e d u s i n g a n i o n i z a t i o n p o t e n t i a l of Ρ =

10.5 e. v . (8) a n d a

P H b o n d e n e r g y i n P H o f 77 k c a l . / m o l e ( 7 ) . 3

W i t h t h e heat f o r m a t i o n o f P H t a k e n to b e 1.3 k c a l . / m o l e ( 7 ) , t h e 3

i o n i c heats of f o r m a t i o n g i v e n i n T a b l e I I a r e c a l c u l a t e d f r o m t h e m e a s u r e d a p p e a r a n c e potentials.


13.

FEHLNER AND CALLEN

Phosphorus

185

Hydrides

Principal Ions from Phosphine, Diphosphine-2, and Diphosphine-4 Appearance

potential, e. v.


This work

Others

10.05 13.2 12.6 15.9

± ± ±

10.2 13.3 11.9

± ± ±

0.2 0.4 0.4

9.17 12.2 11.1 14.6 13.2

0.05 0.2 0.2 0.3 0.2

15.3 17.4 19.4

± ± ± ± ± — ± ± ±

'See See

(13). (14).

f

9

0.05 0.2 0.2 (?)

10.2 13.2 13.3 17.2

10.0 13.9 12.0* 16.7

e

11.5* 14.4 12.4 16.5

d

a

d

a e

e

d

8.7 ± 9.1 10.5" 13.2° 12.2 (10.1) (13.2) (13.4) (17.3)

0.3

10.4' 14.0 ' 13.1' 16.0

€

e

1

10.6» 11.3» 12.7» 13.6» 13.7»

a

a

e

a

0.5 0.5 0.5

12.5

a

e

a

16.7»

a

Uncorrected for multiplier

discrimination.

Diphosphine-2 P H was o r i g i n a l l y p r e p a r e d b y p y r o l y z i n g P H i n the flow reactor s h o w n i n F i g u r e 1 ( 2 ) . L a t e r i t w a s f o u n d that the steady-state c o n c e n t r a t i o n of P H f o r m e d f r o m P H at r o o m t e m p e r a t u r e a n d l o w pressures u s i n g a n e a r l y static system was sufficient to s t u d y this m o l e c u l e . P H has n o t b e e n i s o l a t e d i n a p u r e state, a n d c o n s e q u e n t l y its mass spect r o m e t r y is i n c o m p l e t e . 2

2

2

2

2

2

4

4

2

2

T h e results o n this m o l e c u l e are g i v e n i n T a b l e I. T h e r e l a t i v e a b u n d a n c e s for P H g i v e n here are s o m e w h a t different f r o m t h e a p p r o x i m a t e values r e p o r t e d p r e v i o u s l y ( 2 ) . T h e f o r m e r w e r e o b t a i n e d b y s u b t r a c t i n g the r o o m t e m p e r a t u r e s p e c t r u m of p u r e P H f r o m t h e r o o m t e m p e r a t u r e s p e c t r u m of a m i x t u r e of P H a n d P H , w h i l e the latter w e r e o b t a i n e d b y s u b t r a c t i n g the r o o m t e m p e r a t u r e s p e c t r u m f r o m a h i g h t e m p e r a t u r e s p e c t r u m of the m i x t u r e . A s m a l l t e m p e r a t u r e effect i n the s p e c t r u m of P H c o u l d easily account for the difference o b s e r v e d , a n d the values r e p o r t e d here are the better values. T h e i o n i z a t i o n p o t e n t i a l of P H w a s d e t e r m i n e d u s i n g the s e m i - l o g t e c h n i q u e a n d is less c e r t a i n t h a n the other i o n i z a t i o n potentials. W h e n 2

2

2

2

2

4

2

4

2

4

2

2


186

MASS S P E C T R O M E T R Y

Table I I .

IN INORGANIC C H E M I S T R Y

Calculated Appearance Potentials and Heats of Formation Ion Phosphine

PH PH PH P

3 2

Process PH PH PH PH

+ +

+

+

Diphosphine-2

P.,Ho ΡΓ,Η P 2


Diphosphine-4

+

Ρ.,Η/ P H P Ho P H P PH./ 2

3

2

2

P

Ε

(Ρ—Η)

+

+

+

+

3 2

+ H + H + H + H

+

+

2

+

3

2

2

2

2

2

2

2

4

2

4

2

4

2

4

2

-» P H -> P , H -> P 2

2

-» -* -» -> -»

4

+

PH

3

P H P H P*H P H P H PoH

+

+

9

3

P H P H P H

+

7

-> P H -> P H -» PH -> P

3

2

+

+ Η + H

+

+

P.>H P H/ P,H./ P H P PH/ PH/ PH/ PH PH PH PH P* P P P 2

+

2

2

(a) (b) ~> (c) -> (a) P.>H ~> (b) -> (c) (d) -» (a) P , H -> (b) -» (c) -> (d) -» 4

+

+

4

+

+

+

4

+

+

+

+ + + + + + + + + 4+ + + + +

Η H H + Η 2H PH Ρ+ H PH + Η PH P H + H., PH + Η Ρ+ H + Η PH + H PH + Η Ρ+ H + H P H + Ho + Η 2

2

2

2

2

3

2

2

2

2

3

2

3.2 e. v. is u s e d for the ions, the e s t i m a t e d

=

2

+ 4

2

appearance

potentials are consistent w i t h the m e a s u r e d values for the chosen

proc

esses. T h e heats of f o r m a t i o n of the ions for these processes are g i v e n i n T a b l e II i n terms of the heat of f o r m a t i o n of P H . 2

2

Diphosphine-4 P H 2

4

w a s p r e p a r e d as p r e v i o u s l y d e s c r i b e d

(I).

T h e results of t h i s

s t u d y a l o n g w i t h those of the other t w o studies (14, T a b l e I.

T h e r e l a t i v e i n t e n s i t y of P H

3

+

from P H 2

4

are g i v e n i n

17)

is a m a x i m u m v a l u e

as t h e a p p e a r a n c e p o t e n t i a l m e a s u r e m e n t for this i o n s h o w e d the presence of a s m a l l P H obtained.

A

3

i m p u r i t y . N o g o o d v a l u e for A ( P H

comparison

of

3

+

/ P H ) could 2

4

the f r a g m e n t a t i o n p a t t e r n o b t a i n e d

be

with

collision-free s a m p l i n g a n d those r e p o r t e d p r e v i o u s l y for

conventional

s a m p l i n g shows c l e a r l y t h a t d e c o m p o s i t i o n

spectrometer

occurs i n the

source. T h e i o n i z a t i o n p o t e n t i a l r e p o r t e d here does not agree w e l l w i t h either of the p r e v i o u s values (14, 17).

A tentative explanation m a y be


13.

FEHLNER AND CALLEN

Phosphorus

187

Hydrides

of Ions from Phosphine, Diphosphine-2, and Diphosphine-4 Calculated appearance potential e. v.

AH kcal./mole +

f

233 254 291 316

13.2 12.0 15.2,15.9

235 + Δ Η , ( P H ) 254 + A H ( P H ) 274 + Δ Η ( P H ) 2


13.4 12.1

2

f

2

2

£

2

2

216 234 261 289 309

12.4 11.1 14.3 13.0 12.0 14.1 15.2 12.4 14.6 15.8 17.8 14.6 15.8 16.8 18.0

p u t f o r t h o n the basis of the shape of the i o n i z a t i o n efficiency

curve.

F r o m F i g u r e 2 one sees that t h e i o n efficiency c u r v e f o r d i p h o s p h i n e - 4 w i l l e x h i b i t c o n s i d e r a b l y m o r e " t a i l i n g " t h a n the rare gas c u r v e . A close l o o k at the m e t h o d s

(8)

shows that the l i n e a r e x t r a p o l a t i o n t e c h n i q u e

w i l l y i e l d a h i g h i o n i z a t i o n p o t e n t i a l , a n d the e n e r g y c o m p e n s a t i o n t e c h n i q u e w i l l g i v e a l o w v a l u e . S a a l f e l d a n d Svec u s e d the f o r m e r m e t h o d and obtained a h i g h ionization potential, w h i l e W a d a a n d Kiser used the latter a n d o b t a i n e d a l o w result. Once again using E ( P — H ) = p e a r a n c e potentials for the P

2

3.2 e. v. for the ions, the e s t i m a t e d a p

H / ions are consistent w i t h the chosen p r o c

esses a n d the m e a s u r e d values. T a k i n g the heat of f o r m a t i o n of P H 2

4

to be

5.0 k c a l . / m o l e ( 7 ) the i o n i c heats of f o r m a t i o n are c a l c u l a t e d . C o m b i n i n g the values for P H 2

and P H

4

2

the best v a l u e b e i n g 26 ±

2

y i e l d s the heat of f o r m a t i o n of

P H , 2

2

8 kcal./mole.

T h e A ( P H / / P H ) values are r a t h e r u n c e r t a i n . S i n c e these values 2

4

h a v e b e e n p r e v i o u s l y u s e d to d e r i v e b o n d energies ( 1 5 ) , it is of interest to estimate the a p p e a r a n c e potentials of the v a r i o u s processes. T h i s c a n b e d o n e u s i n g the heats of f o r m a t i o n of the P H . / ions f r o m T a b l é I I , t h e



188

MASS S P E C T R O M E T R Y IN INORGANIC C H E M I S T R Y

heats of f o r m a t i o n of H a n d Ρ (12), D(P—Η)

—

E(P—H) —

a n d b y assuming D ( H P — H )

=

2

77 k c a l . / m o l e

(7).

T h e results g i v e n i n

T a b l e I I s h o w that the m e a s u r e d a p p e a r a n c e potentials are not consistent w i t h t h e l o w e s t e n e r g y processes. I n p a r t i c u l a r , it appears that P H

2

is

+

f o r m e d b y process c w i t h n o excess energy or b y process b w i t h 1.2 e. v. excess energy r a t h e r t h a n b y process a as p r e v i o u s l y a s s u m e d

(15).

T h e s u b s t a n t i a l disagreement b e t w e e n the results of this s t u d y a n d the p r e v i o u s studies c a n b e e x p l a i n e d i n terms of d e c o m p o s i t i o n of P H 2

i n the mass spectrometer

source.

shows that p r o d u c t i o n of P H P H 2

4

S

C o m p a r i n g fragmentation

explains the difference b e t w e e n

4

patterns Α(ΡΗ//

) values r e p o r t e d b y W a d a a n d K i s e r a n d the values r e p o r t e d here.

It also p r o b a b l y accounts for the l o w values of S a a l f e l d a n d Svec. T h e d i s a g r e e m e n t for P H . / ions is not as easily e x p l a i n e d . T a b l e I 2

shows that there is a d i s t i n c t s i m i l a r i t y i n W a d a a n d K i s e r ' s values for


13.

PhosphofUS

FEHLNER AND CALLEN

189

Hydrides

A ( P H 7 P H ) , A ( P H 7 P H ) , a n d A ( P / P H ) , a n d t h e values for the same ions f r o m P2H d e t e r m i n e d here. T h i s was a n i n d i c a t i o n t h a t i n a d d i t i o n to P H , P H w a s f o r m e d i n the source. 2

2

2

4

2

2

4

2

+

2

4

2

3

2

2

T o test this, the f o l l o w i n g e x p e r i m e n t w a s c a r r i e d out. T h e a p p e a r ance potentials of ions f r o m P H w e r e m e a s u r e d u s i n g t h e energy c o m p e n s a t i o n t e c h n i q u e ( t h e m e t h o d of W a d a a n d K i s e r ) a n d u s i n g t h e m o d u l a t e d m o l e c u l a r b e a m s a m p l i n g system. T h e mass spectrometer w a s t h e n s w i t c h e d over to o p e r a t i o n i n the u n m o d u l a t e d m o d e w i t h t h e shutter closed to a p p r o x i m a t e the o p e r a t i n g c o n d i t i o n s of W a d a a n d K i s e r . T h e a p p e a r a n c e potentials w e r e d e t e r m i n e d b o t h b y the energy c o m p e n s a t i o n a n d the v a n i s h i n g c u r r e n t techniques. T h e results are given i n Table III. Downloaded by CORNELL UNIV on May 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch013

2

Table III.

Appearance Potentials of Ions from Diphosphine-4 for Beam and Conventional Sampling Modulated Beam e. c.

Ion P H P H P H

Unmodulated e. c.

v. c.

Ref. 17 e. c.

3

2

2

12.4 ± 0.3 11.1 14.6 13.2

+ +

12.0 ± 0.3 10.8 13.7 12.2

11.8 ± 0.3 10.2 13.6 11.8

9.1 ± 0.3 10.5 13.2 12.2

+

b

a

a

2

2

4

a

. refers to energy compensation technique, . refers to vanishing current technique. W i t h i n e x p e r i m e n t a l e r r o r the values d e t e r m i n e d b y the e n e r g y c o m p e n s a t i o n t e c h n i q u e i n the m o d u l a t e d case agree w i t h those i n T a b l e I l i s t e d u n d e r this w o r k . I n the u n m o d u l a t e d case the m e a s u r e d a p p e a r ance potentials of P H , Ρ2ΓΓ, a n d P are i d e n t i c a l to those of P H . I t m a y b e c o n c l u d e d t h e n that P H was present i n W a d a a n d K i s e r s source, a n d the best values for the a p p e a r a n c e potentials of these ions f r o m P2H4 are those r e p o r t e d i n T a b l e I for this research. %

2

2

+

2

2

+

2

2

2

T h e last e x p e r i m e n t also shows that the a p p e a r a n c e p o t e n t i a l of P H is the same i n b o t h t h e m o d u l a t e d a n d u n m o d u l a t e d cases, a n d the l o w v a l u e r e p o r t e d b y W a d a a n d K i s e r is not c o n f i r m e d . It is possible that the P 2 H , w h i c h t h e y suggest is present i n t h e i r source, w a s p r o d u c e d b y a surface r e a c t i o n o n the w a l l s or filament a n d c o n s e q u e n t l y d e p e n d s r a t h e r specifically o n the source c o n d i t i o n s . I t m a y b e n o t e d that t h e pressure i n the source u s e d here w a s 2 X 10" t o r r d u r i n g o p e r a t i o n w h i c h is p r o b a b l y a factor of 10 less t h a n t h e pressure i n W a d a a n d K i s e r s source. A l s o the s i m u l a t e d c o n v e n t i o n a l s p e c t r u m o b t a i n e d i n this e x p e r i m e n t shows less P H t h a n does the s p e c t r u m of W a d a a n d Kiser. 2

3

+

3

7

3

F i n a l l y , i t is not c o m p l e t e l y clear w h y t h e a p p e a r a n c e potentials r e p o r t e d b y S a a l f e l d a n d Svec (14,15) differ f r o m b o t h those g i v e n h e r e


190

MASS SPECTROMETRY I N INORGANIC

CHEMISTRY

a n d f r o m those o f W a d a a n d K i s e r . O n e notes t h a t w i t h o n e e x c e p t i o n t h e differences i n A ( P H 2

x

+

)-A (P H 2

4

+

) r e p o r t e d b y S a a l f e l d a n d Svec a r e

t h e same w i t h i n e x p e r i m e n t a l error t o those r e p o r t e d b y W a d a a n d K i s e r . I f o n e m a k e s t h e ad hoc a s s u m p t i o n that t h e former's voltage scale c a l i b r a t i o n w a s i n error o w i n g t o t h e u s e o f t h e l i n e a r e x t r a p o l a t i o n m e t h o d , then they too were probably observing a mixture of pyrolysis products. T h e m a g n i t u d e of t h e P

2

+

i o n i n t e n s i t y suggests t h a t i n this case P

4

was

one o f t h e p r o d u c t s . Acknowledgments


T h i s w o r k w a s supported i n major part b y the N a t i o n a l

Science

F o u n d a t i o n , grant N S F - G P - 4 1 8 6 . P a r t i a l s u p p o r t o f t h e R a d i a t i o n L a b o r a t o r y o f t h e U n i v e r s i t y o f N o t r e D a m e w h i c h is o p e r a t e d u n d e r contract w i t h t h e U . S. A t o m i c E n e r g y C o m m i s s i o n is also a c k n o w l e d g e d .

T h i s is

A E C Document N o . COO-38-513. Literature

Cited

(1) (2) (3) (4) (5)

Evers, E. C., Street, Ε. H., Jr., J. Am. Chem. Soc. 78, 5726 (1956). Fehlner, T. P.,J.Am. Chem. Soc. 88, 1819 (1966). Fischler, J„ Halmann, M., J. Chem. Soc. 1964, 31. Fite, W. L., Brackmann, R. T., Phys. Rev. 112, 1141 (1958). Foner, S. N., Hudson, R. L., J. Chem. Phys. 21, 1374 (1953); 36, 2676 (1962). (6) Fox, R. E., Hickam, W. M., Grove, D. T., Kjeldaas, T., Jr., Rev. Sci. Instr. 26, 1101 (1955). (7) Gunn, S. R., Green, L. G., J. Phys. Chem. 65, 779 (1961). (8) Kiser, R. W., "Introduction to Mass Spectrometry and Its Applications," pp. 168-169, Prentice-Hall Inc., Englewood Cliffs, N . J., 1965. (9) McDowell, C. Α., Ed., "Mass Spectrometry," pp. 553-564, McGraw-Hill Book Co., Inc., New York, Ν. Y., 1963. (10) Melton, C. E., Hamill, W. H., J. Chem. Phys. 41, 3464 (1964). (11) Neuert, H., Clasen, H., Z. Naturforsch. 7a, 410 (1952). (12) Rossini, F. D., et al, "Selected Values of Chemical Thermodynamic Properties," Circular of the NBS, No. 500, 1952. (13) Saalfeld, F. E., Svec, H. J., Inorg. Chem. 2, 46 (1963). (14) Ibid., 2, 50 (1963). (15) Ibid., 3, 1442 (1964). (16) Talrose, V. L., et al., Prib. i Tekhn. Experim. 6, 78 (1960). (17) Wada, Y., Kiser, R. W., Inorg. Chem. 3, 174 (1964). (18) Watanabe, K., Mottl, R., J. Chem. Phys. 26, 1773 (1957). RECEIVED October 11, 1966.


Mass Spectrometry in Inorganic Chemistry

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