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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 .
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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.
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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'
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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.
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
13.
FEHLNER AND CALLEN
Phosphorus
185
Hydrides
Principal Ions from Phosphine, Diphosphine-2, and Diphosphine-4 Appearance
potential, e. v.
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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
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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.
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
