5 Direct Mass Spectrometric Sampling of
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
High Pressure Systems THOMAS A.
MILNE
and
FRANK
T.
GREENE
Midwest Research Institute, Kansas C i t y , M o .
The
extension
inorganic
of
systems
direct
mass spectrometric
at higher
pressures
the type of species and reactions method
involves
subsequently
nucleation.
including
A three-stage,
observation behavior
of clusters of Hg
preliminary species
Ar
2
and CsCl
indicates
beam. and
differentially and
in Ar and
that collisions
energies and densities
princi-
homogeneous sampling
of flames, to
to the N
2
study
carrier
the
of
the
gases.
of growth
between are
the
pumped
of the kinetics
is
Knowledge
to predict
to the sampling in argon,
consideration
low thermal
is sufficient
mass separation
system has been applied
One
as a free jet, which
into a molecular
of such free-jet expansions pal phenomena,
to in
that can be studied.
an initial expansion
collimated
sampling
offers advantages
A
of
the
molecules
at
important.
" \ T a s s s p e c t r o m e t r y has p r o v e d to be a n extremely versatile detector i n the s t u d y of i n o r g a n i c gaseous systems, as the papers i n this s y m p o s i u m i n d i c a t e . M o s t of the systems s t u d i e d b y d i r e c t line-of-sight s a m p l i n g of r e a c t i v e species, h o w e v e r , h a v e b e e n at r e l a t i v e l y l o w pressures. T h e r e are several reasons for w i s h i n g to extend d i r e c t mass spect r o m e t r i c s a m p l i n g to systems at h i g h e r pressure. B r e w e r ( 5 ) has p o i n t e d out t h a t the c o m p l e x i t y of the v a p o r i n e q u i l i b r i u m w i t h a
condensed
phase f r e q u e n t l y increases w i t h i n c r e a s i n g t e m p e r a t u r e a n d h e n c e i n c r e a s i n g pressure. T h u s , one m a y find, a n d b e a b l e to study, m a n y n e w species at h i g h e r pressures.
A n e x a m p l e is f u r n i s h e d b y the class of
w e a k l y b o u n d v a n der W a a l s ' d i m e r s w h i c h exist i n a l l gases, w i t h the possible exception of H e . F u r t h e r m o r e , b o t h h o m o g e n e o u s a n d heterogeneous e q u i l i b r i a often m u s t b e d r i v e n b y a h i g h p a r t i a l pressure of r e a c t i n g gas to o b t a i n a p p r e c i a b l e concentrations of a p a r t i c u l a r species. T h e case of steam over N a C l ( c ) g i v i n g a p o s t u l a t e d N a C l * 7 H 0 gaseous 2
68
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
5.
M I L N E A N D GREENE
High Pressure
69
Systems
m o l e c u l e ( 7 ) is a n e x a m p l e . A n o t h e r process of some interest is t h a t of h o m o g e n e o u s n u c l e a t i o n of b o t h l o w a n d h i g h t e m p e r a t u r e species, w h i c h is observable i n its earliest m o l e c u l a r stages i n the e x p a n s i o n i n t o a v a c u u m t h a t occurs i n d i r e c t h i g h pressure s a m p l i n g .
Finally,
many
p r a c t i c a l c h e m i c a l processes o c c u r i n h i g h pressure e n v i r o n m e n t s . A s a n e x a m p l e , i t is c u r r e n t l y a m a t t e r of some c o n c e r n w h e t h e r the species w h i c h h a v e b e e n s h o w n to b e i m p o r t a n t i n the l o w pressure o x i d a t i o n of Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
m e t a l s , t h e l o w pressure d e c o m p o s i t i o n
a n d c o m b u s t i o n of s o l i d p r o -
pellants, a n d the l o w pressure e q u i l i b r i a of l i g h t m e t a l c o m p o u n d s , s t i l l the i m p o r t a n t species
at the h i g h e r pressures a n d
are
temperatures
i n v o l v e d i n p r a c t i c a l c o m b u s t i o n systems. I n the f o l l o w i n g sections w e discuss m o l e c u l a r b e a m f o r m a t i o n f r o m a h i g h pressure gas. H i g h pressure here refers to a n y s a m p l i n g c o n d i t i o n i n w h i c h the m e a n free p a t h of the gas, λ, is s u b s t a n t i a l l y s m a l l e r t h a n t h e s a m p l i n g orifice d i a m e t e r , d—i.e.,
the K n u d s e n n u m b e r , K„ =
λ/d,
is m u c h less t h a n 1. O n l y the s a m p l i n g of n e u t r a l gases w i l l b e c o n s i d e r e d . S o m e of the p h e n o m e n a discussed h a v e a b e a r i n g o n the d i r e c t s a m p l i n g of ions, b u t the s p e c i a l p r o b l e m s of i o n e x t r a c t i o n w i l l not b e discussed.
Beam Formation Process Free-Jets. I n c o n v e r t i n g a h i g h pressure gas i n t o a m o l e c u l a r b e a m w h i c h c a n b e i n t r o d u c e d i n t o the i o n source of a mass spectrometer, t h e c r u c i a l changes i n c o m p o s i t i o n or state o c c u r d u r i n g t h e i n i t i a l c o n t i n u u m e x p a n s i o n w h i c h occurs s a m p l i n g orifice.
downstream
(and slightly upstream)
of
the
If the pressure d o w n s t r e a m f r o m the orifice is k e p t
q u i t e l o w , t y p i c a l l y 10" or 10" of the pressure of the gas b e i n g s a m p l e d , r>
fi
one obtains a free-jet
Free-jets are r e c e i v i n g m u c h
study
c u r r e n t l y because of t h e i r p e r t i n e n c e to the K a n t r o w i t z - G r e y (14)
expansion.
type
of supersonic beams for p r o d u c i n g h i g h energy, h i g h i n t e n s i t y m o l e c u l a r fluxes
and
because t h e y c a n p r o v i d e a supersonic flow field of k n o w n
properties for v a r i o u s a e r o d y n a m i c tests. T h e p r o b l e m of h i g h pressure s a m p l i n g , of course, p r o v i d e s a t h i r d m o t i v a t i o n for u n d e r s t a n d i n g freejets. T h e details of free-jet s t r u c t u r e a n d properties are g i v e n i n m a n y recent papers, p a r t i c u l a r l y those i n the p r o c e e d i n g s of the R a r e f i e d G a s D y n a m i c s S y m p o s i a (6). p e r t i n e n t (2, 3, 8,15).
I n a d d i t i o n , s e v e r a l recent r e v i e w articles are
O n l y those aspects of i m m e d i a t e c o n c e r n to d i r e c t
s a m p l i n g w i l l b e discussed here. A s a basis for u n d e r s t a n d i n g the s a m p l i n g process, it is reasonable to a p p r o x i m a t e the c e n t e r - l i n e flow of gas f r o m a k n i f e - e d g e d orifice as c o n s i s t i n g of a c o n t i n u u m a d i a b a t i c i s e n t r o p i c e x p a n s i o n u p to a t r a n s i t i o n p o i n t at w h i c h it a b r u p t l y enters a n essentially collisionless r e g i o n . C l e a r l y , this is not accurate since the a c t u a l t r a n s i t i o n is g r a d u a l , yet t h e
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
70
MASS SPECTROMETRY
I N INORGANIC
CHEMISTRY
s i m p l e m o d e l has p r o v e d u s e f u l i n c o r r e l a t i n g free-jet d a t a . D i r e c t e x p e r i m e n t a l d a t a f o r s m a l l orifices a n d m o n a t o m i c gases g i v e t h e M a c h n u m b e r of t h e gas as a r e s u l t of t h e c o n t i n u u m e x p a n s i o n a n d c a n b e fit t o a n effective t e r m i n a l M a c h n u m b e r a t w h i c h c o l l i s i o n s essentially cease ( I , 25).
O v e r t h e c o n t i n u u m p o r t i o n of t h e e x p a n s i o n , A s h k e n a s a n d S h e r
man
( 6 ) g i v e t h e c a l c u l a t e d M a c h n u m b e r as a f u n c t i o n of d i s t a n c e
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
downstream as: M w h e r e y is t h e r a t i o of specific heats, d is t h e orifice d i a m e t e r , a n d χ is t h e d i s t a n c e d o w n s t r e a m f r o m t h e orifice. A a n d x h a v e t h e f o l l o w i n g v a l u e s 0
for different y's: y
A
x /d
5/3 7/5 9/7
3.26 3.65 3.96
0.075 0.40 0.85
A t l a r g e distances M
P
/
P
o
=
w h i c h for γ =
(
1 +
0
A(xfd)^'
1
7-ZJLM»)
«
W
( ^ ) "
1
/
7
l
A - 2 / T - i ( x / d ) - 2
5 / 3 reduces t o :
p / p 0
=
( 2 )
9
w h e r e p is t h e source d e n s i t y a n d ρ is t h e d e n s i t y a t a d i s t a n c e χ f r o m 0
the orifice of d i a m e t e r d. diameters.)
( N o t e t h a t t h e e x p a n s i o n is s c a l e d i n orifice
S t a n d a r d expressions
for isentropic expansion i n
flowing
systems relate t h e M a c h n u m b e r o r d e n s i t y t o t h e l o c a l pressure, t e m p e r a t u r e , a n d v e l o c i t y . I t is i n t e r e s t i n g t h a t t h e flow is s o u r c e l i k e a n d differs r e l a t i v e l y l i t t l e i n t h e rate of d e n s i t y decrease f r o m t h e rate g i v e n b y t h e K n u d s e n effusion expression ( 2 8 ) w e r e t h i s r e l a t i o n s h i p to a p p l y o v e r t h e same source c o n d i t i o n s . _
0.0625
\P/Po) Knudsen — J^Jfiyai
'
^ '
P r e d i c t i o n of t h e t h e o r e t i c a l b e a m i n t e n s i t y at a l a r g e d i s t a n c e f r o m t h e orifice, w i t h
i n t e r v e n i n g slits, r e q u i r e s
consideration
of the terminal
M a c h n u m b e r a n d t h e g e o m e t r y of t h e s e c o n d slit. W i t h a sufficiently l a r g e s e c o n d slit, o r s k i m m e r , A n d e r s o n a n d F e n n (4) A s h k e n a s a n d S h e r m a n ' s source-flow
expression
have argued that
(Equation 2) can be
a p p l i e d at a n y d i s t a n c e , e v e n i n t o t h e essentially collisionless r e g i m e .
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
5.
M I L N E A N D GREENE
High
Pressure
71
Systems
T h u s , a n u p p e r l i m i t to a t t a i n a b l e b e a m intensities is p r o v i d e d i f d e p a r tures f r o m i d e a l i t y a n d scattering are n e g l i g i b l e . A n d e r s o n , A n d r e s , a n d F e n n (3)
give a n expression for i n t e n s i t y i n the case of a v e r y s m a l l
skimmer and a terminal M a c h number, M . Likewise, Anderson and T
F e n n (4)
g i v e a n expression for large s k i m m e r s .
T h e most d e f i n i t i v e
d i s c u s s i o n of b e a m intensities appears to b e that of H a g e n a a n d M o r t o n (23).
Experimental beam
intensities o b t a i n e d i n o u r system w i l l
be
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
c o m p a r e d w i t h those c a l c u l a t e d f r o m E q u a t i o n 2 i n the next section. F o r m o n a t o m i c gases, the e x p a n s i o n is r e l a t i v e l y s i m p l e ; o n l y t r a n s l a t i o n a l degrees of f r e e d o m exist, a n d n o t w i t h s t a n d i n g s u c h refinements as c o n s i d e r a t i o n of n o n i s e n t r o p i c flow a n d a n i s o t r o p i c a n d n o n - M a x w e l l i a n v e l o c i t y d i s t r i b u t i o n s ( 1 3 ) , the s i m p l e p i c t u r e a b o v e s h o u l d g i v e a u s e f u l d e s c r i p t i o n of the h i s t o r y of the s a m p l e d gas.
It is a s s u m e d , of
course,
that n o h o m o g e n e o u s n u c l e a t i o n is o c c u r r i n g d u r i n g e x p a n s i o n
(dis-
cussed l a t e r ) . W i t h p o l y a t o m i c gases one m u s t c o n s i d e r the r e l a x a t i o n of the v a r i o u s i n t e r n a l degrees of f r e e d o m d u r i n g the e x p a n s i o n .
Direct
e x p e r i m e n t a l d a t a o n the t r a n s l a t i o n a l ( I , 2 5 ) a n d r o t a t i o n a l states 24)
(18,
d u r i n g expansion have been obtained b y velocity distribution mea-
surements a n d b y o p t i c a l spectroscopy.
T h e v i b r a t i o n a l b e h a v i o r has b e e n
i n f e r r e d f r o m the a p p a r e n t y w h i c h describes the m e a s u r e d free-jet p r o p erties.
A s a first a p p r o x i m a t i o n one c a n p r e d i c t c o m p l e t e t r a n s l a t i o n a l
r e l a x a t i o n to the t e r m i n a l M a c h n u m b e r c o n d i t i o n ( a m a t t e r of d e f i n i tion).
Rotational relaxation w i l l be
temperatures
considerable, but
final
rotational
are s u b s t a n t i a l l y h i g h e r t h a n t r a n s l a t i o n a l temperatures.
V i b r a t i o n a l r e l a x a t i o n w i l l u s u a l l y be m i n i m a l .
F o r excited
electronic
states, r a d i a t i v e processes w i l l p r o b a b l y d o m i n a t e over c o l l i s i o n a l d e excitation.
W h e n collisions h a v e essentially s t o p p e d , t h e state of
the
m o l e c u l e s w i l l r e m a i n f r o z e n w i t h the possible e x c e p t i o n of u n i m o l e c u l a r reactions s u c h as those p o s t u l a t e d b y R o b b i n s a n d L e c k e n b y ( 1 6 ) , i n w h i c h w e a k l y b o u n d p o l y a t o m i c clusters essentially rotate
themselves
a p a r t i n the absence of collisions. T h e a c t u a l course of the free-jet e x p a n s i o n is s h o w n i n F i g u r e 1 f o r three gases, A r , N , a n d C H , i n i t i a l l y at 1 a t m . a n d 3 0 0 ° K . T h e curves 2
4
l a b e l e d "free-jet" s h o w the pressure-temperature c o n d i t i o n s of i s e n t r o p i c e x p a n s i o n . T h e t e r m i n a l M a c h n u m b e r for a r g o n c a n b e p r e d i c t e d f r o m Anderson and Fenn's criterion
(4). (4)
T h e three n e a r l y straight lines s h o w the e q u i l i b r i u m v a p o r pressure of the c o n d e n s e d phases of the three gases. T h e significance of these curves w i l l b e c o m e a p p a r e n t i n the d i s c u s s i o n of n u c l e a t i o n . D o u b l i n g of the orifice size, for a g i v e n pressure, w o u l d h a v e t w o effects.
F i r s t , the t e r m i n a l
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
72
MASS SPECTROMETRY I N INORGANIC
CHEMISTRY
M a c h n u m b e r w o u l d increase a c c o r d i n g to E x p r e s s i o n 4. S e c o n d , the t i m e r e q u i r e d to r e a c h a g i v e n T-P
p o i n t o n the curves, c o r r e s p o n d i n g to a
given M a c h number, w o u l d double.
T i m e s of the o r d e r of
microseconds
are i n v o l v e d over the ranges s h o w n i n the figure w i t h orifice sizes of a few mils. It s h o u l d b e e m p h a s i z e d a g a i n that a l l the a b o v e d i s c u s s i o n assumes a n i d e a l e x p a n s i o n a n d the absence of shock effects, either i n the free-jet Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
or as a result of the presence of the s k i m m e r i n the flow field of the orifice. T h e v a l i d i t y of these assumptions i n o u r s a m p l e r is d i s c u s s e d
elsewhere
(9,10). ι ο
ARGON
•
N
Δ
CH
2
4
FREE JET EXPANSION VAPOR PRESSURE OF CONDENSED PHASE
X= /3 5
y = /£ 7
8 2\ x 10 ) °κ
('/τ
JL
10
12
14
Figure 1. A comparison of calculated free-jet expansion history with saturated vapor pressures for Ar, N„ and CH, initially at 1 aim. and 300 K. t
S
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
5.
M I L N E A N D GREENE
High Pressure
73
Systems
Sampling Effects Accompanying Free-Jet Expansion. T h e r e are a n u m b e r of i m p o r t a n t consequences of d i r e c t free-jet s a m p l i n g . F i r s t , i n s a m p l i n g m i x t u r e s of gases, a w e l l d e v e l o p e d c o n t i n u u m expansion w i l l result i n a n e a r l y u n c h a n g e d c o m p o s i t i o n of gas at the t r a n s i t i o n r e g i o n (26)
w i t h a l l molecules m o v i n g a l o n g the b e a m axis w i t h essentially the
same v e l o c i t y .
T h e m o l e c u l e s of different m o l e c u l a r w e i g h t w i l l
have
d i f f e r i n g r a n d o m t h e r m a l velocities, h o w e v e r , a n d as a w e l l c o l l i m a t e d Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
m o l e c u l a r b e a m is f o r m e d , the l i g h t e r m o l e c u l e s w i l l s p r e a d m o r e r a p i d l y t h a n the heavier. T h e c o n s e q u e n c e , as first p o i n t e d out b y S t e r n , W a t e r man, and Sinclair (27)
a n d verified b y Green, Brewer, a n d M i l n e
is t h a t the m o l e c u l a r b e a m r e a c h i n g the mass-spectrometer
ion
(JO) source
w i l l b e d e p l e t e d i n l i g h t e r molecules i n p r o p o r t i o n to the first p o w e r of t h e i r m o l e c u l a r w e i g h t . T h a t the different m o l e c u l e s w i l l h a v e essentially the same m e a n a x i a l v e l o c i t y has b e e n v e r i f i e d for m i x t u r e s of gases b y a c h o p p e d b e a m , time-of-flight m e t h o d ( 1 2 ) .
F o r example, i n a H e - A r
m i x t u r e s a m p l e d at 1 a t m o s p h e r e t h r o u g h a 0.002 i n c h d i a m e t e r orifice, the A r a n d H e velocities d i f f e r e d b y o n l y a f e w One
percent.
i n t e r e s t i n g c o n s e q u e n c e of the a b o v e v e l o c i t y
phenomenon,
w h i c h has b e e n p o i n t e d out b y A n d e r s o n , A n d r e s , a n d F e n n ( 2 ) , i n terms of
argon-90%
H e m i x t u r e , t h e final b e a m c o m p o s i t i o n w i l l b e a b o u t 5 0 %
argon.
beam-surface
reaction
studies.
For a
has
significance
10%
M o r e i m p o r t a n t , time-of-flight d a t a s h o w that the a r g o n has a
most p r o b a b l e v e l o c i t y e q u i v a l e n t to a n effusive b e a m w i t h a t e m p e r a t u r e 2300°K., e v e n t h o u g h the source t e m p e r a t u r e is 3 0 0 ° K . A l a r g e n u m b e r of m i x t u r e s h a v e b e e n d i r e c t l y s t u d i e d b y A b u a f et al. (1)
illustrating
this feature. A second effect w h i c h occurs i n h i g h pressure s a m p l i n g is r e a l l y just a n e x a m p l e of a f a i l u r e to preserve the concentrations of species o r i g i n a l l y present.
A s F i g u r e 1 shows, e v e n gases w h i c h w e r e o r i g i n a l l y h i g h l y
u n s a t u r a t e d m a y b e c o m e e n o r m o u s l y s u p e r s a t u r a t e d i n the free-jet a n d h o m o g e n e o u s n u c l e a t i o n w i l l result (11, 21).
I n the case of s a m p l i n g of
gases w h i c h are i n i t i a l l y s a t u r a t e d w i t h respect to a c o n d e n s e d phase of s o m e c o m p o n e n t , this p h e n o m e n o n w i l l b e exaggerated.
Such condensa-
t i o n is a n u i s a n c e i n s a m p l i n g a n d m u s t b e suspected i n a n y h i g h pressure s t u d y . O n e w a y to detect this effect w i l l b e m e n t i o n e d later. O f
more
i m p o r t a n c e , h o w e v e r , is the fact that the free-jet presents s u c h a t i m e t e m p e r a t u r e - c o l l i s i o n h i s t o r y that r a p i d c o n d e n s a t i o n processes c a n
be
s t u d i e d i n t h e i r e a r l y , m o l e c u l a r stages. A final p o i n t a b o u t d i r e c t mass spectrometric observations of species f r o m a free-jet is that the i n t e r n a l e n e r g y states of the m o l e c u l e w i l l n o t be precisely k n o w n .
Consequently, w h e n dealing w i t h molecules
from
h i g h t e m p e r a t u r e sources, the f a i l u r e of the v i b r a t i o n a l degrees of f r e e d o m t o r e l a x m a y give rise to f r a g m e n t a t i o n patterns t y p i c a l of h i g h l y e x c i t e d
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
74
MASS SPECTROMETRY I N INORGANIC
molecules.
CHEMISTRY
S u c h effects h a v e a p p a r e n t l y b e e n o b s e r v e d i n the s a m p l i n g
of flames ( 2 0 ) .
A r e l a t e d p r o b l e m is that w i t h the g e n e r a l a b i l i t y to
s a m p l e r e a c t i v e species, c a l i b r a t i o n s for mass spectrometer s e n s i t i v i t y w i l l often not b e a v a i l a b l e a n d one m u s t resort to estimates of sections a n d f r a g m e n t a t i o n b e h a v i o r J
cross
(21). V
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
Hi = =
MASS SPECTROMETER
Γ L— GAS INLET
Figure 2. Schematic of a three-stage, high pressure, molecular beam sampling system using a Bendix time-offlight mass spectrometer as a detector
Apparatus
and
Performance
T h e s a m p l i n g a p p a r a t u s t h a t w e h a v e d e v e l o p e d f o r h i g h pressure studies of i n o r g a n i c systems is s h o w n i n F i g u r e 2. T h i s system has b e e n i m p r o v e d f r o m t h a t d e s c r i b e d i n o u r e a r l i e r w o r k (10), b u t uses t h e same c o m p l e m e n t of p u m p s . T h e orifice-to-electron b e a m distance has b e e n r e d u c e d f r o m 16 to 8 inches, a n d i m p r o v e d p u m p i n g i n e a c h stage has r e s u l t e d i n less b e a m scattering. T y p i c a l o p e r a t i n g c o n d i t i o n s are l i s t e d i n T a b l e I. T h i s system is not u n l i k e other h i g h pressure b e a m a n d s a m p l i n g systems a l t h o u g h of modest p u m p i n g c a p a c i t y . F i g u r e 2 shows a m o t o r - d r i v e n c h o p p e r i n stage t w o , w h i c h has p r o v e d to b e a n essential p a r t of o u r system. T h e advantages, p r o b l e m s , a n d results of u s i n g m o d u l a t e d beams f o r b o t h noise a n d b a c k g r o u n d - i o n d i s c r i m i n a t i o n , as w e l l as time-of-flight v e l o c i t y d e t e r m i n a t i o n s , h a v e b e e n d i s c u s s e d (12). A g r a p h i c i n d i c a t i o n of one of these advantages is g i v e n i n T a b l e I I . H e r e the r a t i o of a n o n c o n d e n s i b l e species, A r , to a v e r y u n s t a b l e species, A r , 2
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
5.
M I L N E AND GREENE
High Pressure
75
Systems
is t a b u l a t e d as a f u n c t i o n of c h o p p i n g f r e q u e n c y . I t is seen t h a t e v e n w i t h a w e l l - c o l l i m a t e d m o l e c u l a r b e a m e n t e r i n g t h e B e n d i x M o d e l 12 i o n i z a t i o n source, d a t a t a k e n w i t h a m a n u a l shutter w o u l d b e i n e r r o r b y a f a c t o r of a b o u t t w o a n d t h a t c h o p p i n g f r e q u e n c i e s of at least 15 c p . s . are n e e d e d to d i s c r i m i n a t e a d e q u a t e l y against b e a m gases scattered i n the i o n source. A n o t h e r a d v a n t a g e of m o d u l a t i o n is t h a t h i g h f r e q u e n c y time-of-flight measurements ( 1 2 ) c a n b e u s e d to d e t e r m i n e the m o s t p r o b a b l e velocities of the b e a m components. V a l u a b l e i n f o r m a t i o n c a n b e d e d u c e d a b o u t t h e extent of the free-jet e x p a n s i o n i n the case of h i g h pressure b e a m f o r m a t i o n a n d a b o u t the m o l e c u l a r w e i g h t of n e u t r a l precursors o f o b s e r v e d ions i n K n u d s e n effusion studies.
Table I.
T y p i c a l Operating Conditions of Molecular Beam Sampling System Exit Slit Dimensions, in.
Pressure, torr Source Stage One Stage T w o Stage Three Ion Source of Bendix M o d e l 12
760 1 3 8 < 1
Typical Scattering Loss, %
8 7-3/4 6-1/2 2-1/8 0
25 15 10
0.002 diam. 0.020 diam. 0.10 X 0.024 0.50 X 0.030
X 10-3 Χ ΙΟ" X 10" Χ ΙΟ"
Table II.
Distance from Ion Source Electron Beam, in.
5
6
6
T h e Dependence of the Observed Ratio A r ^ / A r on Chopping Frequency
Frequency 0 2 8 15 50 100 160
(H ) z
80 /36 +
+
1.45 2.42 2.54 2.64 2.64 2.60 2.62
O u r system has b e e n c a l i b r a t e d to o b t a i n absolute, b e a m fluxes at the i o n source b y c o m p a r i n g the i n t e n s i t y of A r , f r o m a r g o n effusing t h r o u g h a system w i t h k n o w n g e o m e t r y u n d e r K n u d s e n c o n d i t i o n s , w i t h the i n t e n s i t y o b s e r v e d for a s u p e r s o n i c b e a m . I n this w a y b e a m fluxes 8 inches a w a y f r o m the source orifice of a b o u t 5 Χ 1 0 m o l e c u l e s / s q . c m . sec. h a v e b e e n d e m o n s t r a t e d f o r a 0.002 i n c h d i a m e t e r orifice a n d 1 a t m . a r g o n . T h e i n t e n s i t y p r e d i c t e d f r o m E q u a t i o n 2 is 1.3 X 1 0 mole c u l e s / s q . c m . sec. W h e n s c a t t e r i n g corrections of a b o u t 6 0 % are a p p l i e d to the e x p e r i m e n t a l v a l u e , the system approaches to w i t h i n a factor of +
1 5
1 6
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
76
MASS SPECTROMETRY I N INORGANIC
CHEMISTRY
t w o the t h e o r e t i c a l l y p r e d i c t e d m a x i m u m intensity. D y n a m i c ranges of s t u d y of 1 0 h a v e b e e n o b t a i n e d i n the absence of b a c k g r o u n d peaks. I n o u r p r a c t i c a l studies w e are l i m i t e d b y fluctuations of the s i g n a l f r o m the b a c k g r o u n d h y d r o c a r b o n s r a t h e r t h a n e l e c t r o n i c noise. T h e r e is n o o b v i o u s u p p e r l i m i t to the pressure w h i c h c a n b e s a m p l e d p r o v i d e d the c h o i c e of orifice sizes, distances, a n d p u m p i n g speed a l l o w s g o o d free-jet e x p a n s i o n w i t h o u t excessive scattering. W e h a v e f o r m e d beams f r o m 7 a t m . of a r g o n , w h i l e L e c k e n b y et al. (17) h a v e f o r m e d b e a m s f r o m gases at pressures as h i g h as 40 a t m . O n e c o u l d c o n c e i v a b l y s a m p l e fluid systems a b o v e the c r i t i c a l c o n d i t i o n s . T h e most p r o b a b l e l i m i t a t i o n to the c h a r a c t e r i z a t i o n of the a c t u a l m o l e c u l a r species present i n t h e fluid w i l l b e a m b i g u i t i e s b r o u g h t o n b y n u c l e a t i o n p h e n o m e n a . T h e a b i l i t y of a free-jet expansion to q u e n c h c h e m i c a l reactions w i t h p o s i t i v e a c t i v a t i o n energies s h o u l d b e n e a r l y o p t i m a l o w i n g to the ext r e m e l y r a p i d c o o l i n g rates. L i k e w i s e , reactions s u c h as t h a t of c o n d e n sation, w h i c h h a v e a negative t e m p e r a t u r e coefficient, s h o u l d b e q u e n c h e d w i t h m a x i m u m efficiency since, for a g i v e n orifice size, the free-jet e x p a n s i o n results i n the m i n i m u m n u m b e r of collisions d u r i n g the t r a n s i t i o n to m o l e c u l a r flow.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
7
Application
to Inorganic Systems
T h e r e are m a n y a p p l i c a t i o n s of h i g h pressure s a m p l i n g w h i c h w i l l o c c u r to i n o r g a n i c chemists.
W e d e s c r i b e here o n l y those areas w h i c h
are c u r r e n t l y b e i n g p u r s u e d i n o u r l a b o r a t o r y . Flames. O u r w o r k w i t h the d i r e c t s a m p l i n g of flames is representative of a class of s a m p l i n g studies i n w h i c h the s a m p l i n g orifice is not i n t h e r m a l e q u i l i b r i u m w i t h the gaseous system b e i n g s t u d i e d . W e
began
o u r h i g h pressure s a m p l i n g w o r k w i t h the g o a l of s t u d y i n g the t h e r m o d y n a m i c s of gaseous m e t a l - c o n t a i n i n g species at e x t r e m e l y h i g h t e m p e r a tures a n d h i g h p a r t i a l pressures of 0
2
and H 0 .
r e a d i l y a t t a i n a b l e i n the b u r n t gas r e g i o n of
2
S u c h c o n d i t i o n s are
flames.
I n a d d i t i o n , the
a b i l i t y to f o l l o w d i r e c t l y f r e e - r a d i c a l a n d other species t h r o u g h t h e r e a c t i o n z o n e w a s of interest i n terms of the k i n e t i c s t u d y of flame reactions. T h e e q u i l i b r i u m 1-atm. d e t a i l p r e v i o u s l y (20, 22). m a r i z e d as f o l l o w s .
flame
w o r k has b e e n
presented
i n some
T h e present status of this w o r k c a n b e s u m -
It appears that 1-atm. flames as h o t as 4000°K. c a n
b e p r o b e d a n d t h a t f r e e - r a d i c a l a n d other n o n c o n d e n s i b l e species c a n b e q u a n t i t a t i v e l y s a m p l e d . H o w e v e r , w e h a v e b e e n u n a b l e to s a m p l e h i g h l y condensible
species w i t h r e l a t i v e l y c o l d s a m p l i n g orifices.
Isothermal
f u r n a c e studies m e n t i o n e d b e l o w i n d i c a t e that a e r o d y n a m i c effects c a u s e d b y the c o l d orifice a n d o x i d e b u i l d - u p , a n d not the i n h e r e n t h o m o g e n e o u s n u c l e a t i o n or other e q u i l i b r i u m shifts i n v o l v e d i n free-jet expansion, are responsible for this l i m i t a t i o n . A p r o m i s i n g area for f u r t h e r flame w o r k is i n d i c a t e d i n o u r s t u d y of species profiles i n r e a c t i o n zones b y means of the d i r e c t s a m p l i n g of
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
5.
M I L N E AND GREENE
l o w pressure
flames.
High Pressure
77
Systems
T h e l o w pressure serves m a i n l y t o s p r e a d out t h e
r e a c t i o n zone t o a l l o w a d e q u a t e s a m p l i n g r e s o l u t i o n . V e r y s l o w b u r n i n g flames
c o u l d b e s t u d i e d a t o n e atmosphere.
I n a n apparatus described
elsewhere ( 1 9 ) , w e h a v e o b t a i n e d a n u m b e r o f profiles t h r o u g h a l / 2 0 t h atmosphere, l e a n C H - 0 4
2
flame w i t h C H B r a d d e d . 3
T y p i c a l results a r e
s h o w n i n F i g u r e s 3 a n d 4. A b s o l u t e intensities s h o u l d not b e c o m p a r e d between
species, as s e n s i t i v i t y corrections h a v e n o t b e e n m a d e . T h e
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
significance o f these d a t a lies i n t h e g e n e r a l agreement b e t w e e n t h e F i g u r e 3 results a n d p r e v i o u s l y p u b l i s h e d q u a r t z m i c r o p r o b e studies ( 2 9 ) for the stable species, c o m b i n e d w i t h o u r a b i l i t y as s h o w n i n F i g u r e 4 t o f o l l o w the concentrations o f H B r a n d B r . T h e s e latter species h a v e n o t p r e v i o u s l y b e e n s t u d i e d successfully b y i n d i r e c t s a m p l i n g t e c h n i q u e s .
BURNER SCREEN TO
ORIFICE DISTANCE IN CM
Figure 3. Stable species profiles obtained by direct molecular sampling of a l/20th-atm., lean, CH, 0 flame. Flame composition: 89.6% 0 , 10.4% CH r
2
Isothermal Transpiration Cells.
2
H i g h pressures of gas h a v e
h
been
e q u i l i b r a t e d w i t h the c o n d e n s e d phases o f m a n y m a t e r i a l s , i n t h e c o n v e n t i o n a l t r a n s p i r a t i o n e x p e r i m e n t , to p e r m i t t h e s t u d y often o f q u i t e m i n o r v a p o r species. B e c a u s e the i d e n t i f i c a t i o n o f s u c h species is i n d i r e c t , a n d serious c o m p l i c a t i o n s arise i f several gaseous species are present, i t w o u l d b e most d e s i r a b l e t o s a m p l e t h e eifluent d i r e c t l y w i t h a mass spectrometer.
W e a r e d o i n g this b y p l a c i n g a resistance h e a t e d N i
t r a n s p i r a t i o n c e l l i n stage o n e , just b e l o w
t h e s k i m m e r , as s h o w n i n
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
78
MASS SPECTROMETRY I N INORGANIC
CHEMISTRY
F i g u r e 2. O u r present c e l l w h i c h uses orifice d i a m e t e r s of 0.0005 t o 0.004 i n c h w i l l h a n d l e gas pressures u p to 5 a t m . G a s flows are d e t e r m i n e d b y t h e orifice size, for a g i v e n pressure, so several orifice sizes m a y h a v e to b e u s e d to e s t a b l i s h that e q u i l i b r i u m exists. W i t h this system w e are c u r r e n t l y s t u d y i n g the e q u i l i b r i u m L i ( g ) 1/2H
2
+
- » L i H ( g ) , w i t h the i n t e n t i o n of g o i n g o n to o t h e r systems s u c h
as A l +
H
2
w h e r e h i g h e r h y d r i d e s m a y b e present a n d h i g h pressures
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
m a y b e m o r e advantageous i n d e t e c t i n g species of interest. T h e s t u d y of s u c h h i g h pressure e q u i l i b r i a w i l l a l w a y s i n v o l v e the d a n g e r of
free-jet
n u c l e a t i o n , a n d a p p r o p r i a t e tests, s u c h as the one d i s c u s s e d i n the next section, m u s t b e c a r r i e d out.
Figure 4. Profiles of bromine species in a l/20th-atm., lean, CH -0 containing about 1% CH Br. Flame composition: 89.6% 0 , 10.4% h
a
2
2
flame CH, t
Nucleation and the Thermodynamics of Weakly Bound Clusters. W h e n e v e r a c o n t i n u u m e x p a n s i o n is i n v o l v e d i n the s a m p l i n g process, the d a n g e r of s u p e r s a t u r a t i n g a species exists a n d n u c l e a t i o n m a y occur. S u c h n u c l e a t i o n w i l l b e v e r y sensitive to i n i t i a l t e m p e r a t u r e , pressure, a n d to s a m p l i n g orifice size. T h e b e h a v i o r of a r g o n has b e e n s t u d i e d i n some d e t a i l (21).
A p a r t f r o m the c o m p l i c a t i o n s w h i c h n u c l e a t i o n poses
for s a m p l i n g , the mass s p e c t r o m e t r i c s t u d y of free-jet c o m p o s i t i o n
pro-
v i d e s a u n i q u e a p p r o a c h to e l u c i d a t i n g the earliest stages of h o m o g e n e o u s nucleation.
I n fact, the first step i n s u c h c o n d e n s a t i o n , the
r e c o m b i n a t i o n to f o r m a d i m e r species, c a n b e f o l l o w e d .
three-body
Studies of t h i s
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
5.
M I L N E AND GREENE
High Pressure
79
Systems
t y p e are not l i m i t e d to gases s u c h as a r g o n , a n d w e are n o w e x a m i n i n g h i g h e r t e m p e r a t u r e species as w e l l . O n e of the approaches to the i n t e r p r e t a t i o n of t h e A r
2
concentrations
o b s e r v e d i n s a m p l i n g p u r e a r g o n is s h o w n i n F i g u r e 5, w h e r e the o b s e r v e d Ar
2
+
intensities ( a t t r i b u t e d solely to s i m p l e i o n i z a t i o n of A r ) are p l o t t e d 2
against orifice size at fixed pressure.
N o t e the r a t h e r h i g h e x t r a p o l a t e d
c o n c e n t r a t i o n at z e r o orifice d i a m e t e r , w h i c h w e i n t e r p r e t as t h e e q u i Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
l i b r i u m c o n c e n t r a t i o n of A r
i n the static gas
2
(21).
T h e exponential
g r o w t h w i t h orifice size is g o v e r n e d b y n u c l e a t i o n k i n e t i c s d u r i n g the i n c r e a s i n g t i m e a n d d e c r e a s i n g temperatures i n v o l v e d i n e x p a n s i o n f r o m l a r g e r orifices. T h i s d e p e n d e n c e of o b s e r v e d species o n orifice size p r o m ises to b e a n i n d i s p e n s a b l e t e c h n i q u e i n d e t e c t i n g the presence of n u c l e a t i o n effects i n s a m p l i n g . 4,000
"0 1 2 3 4 5 6 ORIFICE DIAMETER IN MILS Figure 5. Ar intensities observed after expansion of argon from 5 atm. and 300°K. through several size orifices +
2
W e are not yet p r e p a r e d to discuss the k i n e t i c significance of t h e e x p o n e n t i a l rise of A r c o n c e n t r a t i o n w i t h orifice size, b u t it is of interest 2
to c o n s i d e r the n a t u r e of the c o l l i s i o n a l - t e m p e r a t u r e h i s t o r y of t h e gas d u r i n g the free-jet expansion.
T a b l e I I I shows the effect of orifice size
o n the t e r m i n a l M a c h n u m b e r , t e r m i n a l t e m p e r a t u r e , a n d n u m b e r
of
t e r n a r y collisions, as c a l c u l a t e d f r o m a s i m p l e k i n e t i c m o d e l b y u s i n g
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
80
MASS SPECTROMETRY I N INORGANIC
temperature-dependent
CHEMISTRY
c o l l i s i o n cross sections a n d a s s u m i n g A n d e r s o n
a n d F e n n ' s c r i t e r i o n of f r e e z i n g for a l l o u r e x p e r i m e n t a l c o n d i t i o n s . f o u r t h c o l u m n lists t h e t o t a l n u m b e r of t e r n a r y collisions p e r
The
molecule
f r o m M a c h 0.50 to the t e r m i n a l M a c h n u m b e r . T h e last c o l u m n lists t h e o b s e r v e d m o l e fractions of A r
2
i n excess of the zero orifice
diameter
e x t r a p o l a t e d values. W i t h o u t d i s c u s s i n g the assumptions m a d e , it is clear that w e are d e a l i n g w i t h collisions b e t w e e n molecules of v e r y l o w r e l a t i v e Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
energy.
F o r e x a m p l e , observe that the n u m b e r of collisions m o r e t h a n
d o u b l e s i n g o i n g f r o m a 0.002 to 0.004 i n c h d i a m e t e r orifice.
I n this
m o d e l , the increase b e y o n d a f a c t o r of t w o is c a u s e d b y the extension of the c o n t i n u u m p a r t of the e x p a n s i o n b y the l a r g e r orifice, as reflected i n the l a r g e r t e r m i n a l M a c h n u m b e r a n d l o w e r t e m p e r a t u r e .
The experi-
m e n t a l A r m o l e fractions also m o r e t h a n d o u b l e f r o m the 0.002 to 0.004 2
i n c h case.
It seems reasonable, t h e n , to relate this excess d i m e r to t h e
collisions w h i c h o c c u r at v e r y l o w temperatures. T h e c o l l i s i o n a l b e h a v i o r i n this r e g i o n is not u n d e r s t o o d at present. A l t h o u g h interpretations m a y b e c o m p l i c a t e d b y s u c h p h e n o m e n a as l o n g - l i v e d o r b i t i n g pairs a n d l a c k of
information
about
the
transition region,
it
seems
well
worth
investigating.
Table III. Calculated Ideal Free-Jet Nucleation History for A r g o n Initially at 3 0 0 ° K . and 5 Atmospheres Orifice Diameter, mils
Terminal Mach No.
Terminal Temp.
Total Ternary Collisions
Observed Excess Mole Fraction of Ar
0.5 1 2 3 4
18.4 24.2 31.9 37.6 42.2
2.6 1.5 0.88 0.64 0.51
71.70 143.58 287.56 431.46 575.48
0.0009 0.0027 0.0075 0.0157 0.0310
2
T h e a b o v e t y p e of c o r r e l a t i o n represents o n l y one of t h e w a y s free-jet n u c l e a t i o n d a t a m a y b e treated.
D i l u t i o n experiments, c o m p a r i s o n
of
expansions s t a r t i n g w i t h different temperatures a n d pressures b u t e n d i n g w i t h the same t e r m i n a l M a c h n u m b e r , a n d other v a r i a t i o n s of the i n i t i a l a n d final states w i l l h e l p i l l u m i n a t e the i m p o r t a n t process of h o m o g e n e o u s n u c l e a t i o n over v a r i o u s t e m p e r a t u r e ranges.
It also seems possible
to
e x t e n d the s t u d y to h i g h e r clusters. T h e n u c l e a t i o n b e h a v i o r of several h i g h e r - t e m p e r a t u r e systems has b e e n e x a m i n e d thus far. A r a n d N
2
h a v e b e e n passed o v e r H 0 , C H O H , 2
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
3
5.
MILNE
AND GREENE
High
Pressure
81
Systems
L i , H g , a n d C s C l at pressures u p to 2 a t m . I n these studies the species A r , A r · H g and H g 2
2
h a v e b e e n o b s e r v e d i n one a t m o s p h e r e of a r g o n
o v e r H g at 500°K. T h e s e d a t a represent c o n t r i b u t i o n s f r o m b o t h e q u i l i b r i u m species a n d those f o r m e d d u r i n g expansion. A c a r e f u l m e a s u r e m e n t of the orifice size d e p e n d e n c e of concentrations s h o u l d a l l o w b o t h a d e t e r m i n a t i o n of the free energy of the d i m e r s a n d a n i n d i c a t i o n of t h e i r k i n e t i c s of f o r m a t i o n . I n t h e case of A r o v e r C s C l , b o t h the m o n o m e r Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
a n d the d i m e r of the salt w e r e d e t e c t e d Knudsen work. In N
2
i n the r a t i o e x p e c t e d
from
the d i m e r w a s r e d u c e d b y a f a c t o r of a b o u t f o u r ;
this u n e x p e c t e d b e h a v i o r is r e c e i v i n g f u r t h e r s t u d y . It s h o u l d b e possible to o b t a i n d i r e c t l y the free energies of a n u m b e r of m i x e d d i m e r s of t h e t y p e A r * C s , C s * H g , etc. M a n y clusters w e r e o b s e r v e d i n the H 0 a n d 2
C H O H systems. T h e case of p o l y a t o m i c m o l e c u l e s m a y b e m o r e c o m p l i 3
c a t e d because of the possible m e t a s t a b i l i t y of the d i m e r s (16).
F o r ex-
a m p l e , w e see several orders of m a g n i t u d e less d i m e r i n N , 0 , a n d N O 2
t h a n one w o u l d at first expect (12).
2
N e v e r t h e l e s s , d i r e c t mass spectro-
m e t r i c v e r i f i c a t i o n of s u c h p o s t u l a t e d species as the H F h e x a m e r a n d t h e m e t h a n o l tetramer m a y b e feasible. F i n a l l y , d i r e c t second l a w heat determ i n a t i o n s of w e a k l y b o u n d d i m e r s also a p p e a r p r a c t i c a b l e .
Summary D i r e c t mass s p e c t r o m e t r i c s a m p l i n g of h i g h - p r e s s u r e systems is p o s s i b l e i n m a n y cases, w i t h a t o l e r a b l e m i n i m u m of c o m p o s i t i o n d i s t u r b a n c e . T h e s t u d y of flames a n d heterogeneous r e a c t i o n systems has s h o w n p r o m ise. A l s o a large class of e q u i l i b r i u m reactions c a n b e e l u c i d a t e d f u r t h e r b y c o m b i n i n g the t r a n s p i r a t i o n e x p e r i m e n t w i t h d i r e c t mass s p e c t r o m e t r i c s a m p l i n g . T h e s t u d y of gases a n d gas m i x t u r e s w i l l g i v e t h e r m o d y n a m i c i n f o r m a t i o n a b o u t v a n d e r W a a l s ' , charge-transfer, a n d h y d r o g e n - b o n d e d species.
F i n a l l y , n u c l e a t i o n , w h i c h is one of the i n h e r e n t p r o b l e m s i n
h i g h pressure s a m p l i n g , c a n b e t u r n e d to a d v a n t a g e b y a l l o w i n g a d e t a i l e d s t u d y of the c o n d e n s a t i o n process o n the m o l e c u l a r scale.
Acknowledgments T h i s w o r k w a s sponsored b y the C h e m i s t r y Office of the A d v a n c e d R e s e a r c h Projects A g e n c y a n d the P o w e r B r a n c h of the Office of N a v a l Research. T h e authors w i s h to a c k n o w l e d g e the h e l p of J a c o b B e a c h e y a n d D o u g l a s D a y i n c a r r y i n g out the e x p e r i m e n t a l p r o g r a m a n d the h e l p of G o r d o n G r o s s i n i n t e r p r e t i n g the results.
G e n e V a n d e g r i f t has
p r i m a r i l y r e s p o n s i b l e for the free-jet, c o l l i s i o n a l - h i s t o r y c a l c u l a t i o n s .
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
been
82
MASS SPECTROMETRY IN INORGANIC CHEMISTRY
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch005
Literature Cited (1) Abuaf, N., Anderson, J. B., Andres, R. P., Fenn, J. B., Miller, D. R., "Rarefied Gas Dynamics," Vol. 2, p. 1317, C. L. Brundin, ed., Academic Press, New York, 1967. (2) Anderson, J. B., Andres, R. P., Fenn, J. B., "Advances in Atomic and Molecular Physics," P. R. Bates, I. Estermann, eds., Vol. I., p. 345, Academic Press, New York, 1965. (3) Anderson, J. B., Andres, R. P., Fenn, J. B., p. 281, "Advances in Chemical Physics," Vol. X, J. Ross, ed., Interscience Publishers, New York, 1966. (4) Anderson, J. B., Fenn, J. B., Phys. of Fluids, 8, 780 (1965). (5) Brewer, L., "Chemistry and Metallurgy of Miscellaneous Materials: Ther modynamics," p. 261, Natl. Nucl. Energy Ser. IV—19B, L. Quill, ed., McGraw-Hill, New York, 1950. (6) de Leeuw, J. H., "Advances in Applied Mechanics Series," Supplement 1 (1961), Supplement 2 (1963), Supplement 3 (1965), Supplement 4 (1967), "Rarefied Gas Dynamics," Academic Press, New York. (7) Elliott, Guy R. B., "Gaseous Hydrated Oxides, Hydroxides, and Other Hydrated Molecules," UCRL-1831, June 1952. (8) French, J. Β., AIAA J. 3, 993 (1965). (9) Greene, F. T., Milne, Τ. Α., "Advances in Mass Spectrometry," Vol. 3, p. 841, The Institute of Petroleum, London, 1966. (10) Greene, F. T., Brewer, J., Milne, Τ. Α.,J.Chem. Phys. 40, 1488 (1964). (11) Greene, F. T., Milne, Τ. Α., J. Chem. Phys. 39, 3150 (1963). (12) Greene, F. T., Milne, Τ. Α., 22nd Quart. Tech. Rept, Contract Nonr3599(00), May 1967. (13) Hamel, B., Willis, D. R., Phys. of Fluids 9, 829 (1966). (14) Kantrowitz, Α., Grey, J., Rev. Sci. Instr. 22, 328 (1951). (15) Knuth, E. L., Appl. Mech. Rev. 17, 751 (1964). (16) Leckenby, R. E., Robbins, E. J., Proc. Roy. Soc. 291, 389 (1966). (17) Leckenby, R. E., Robbins, E. J., Trevalion, P. Α., Proc. Roy. Soc. (Lon don) 280A, 409 (1964). (18) Marrone, V., Univ. Toronto, Inst. Aerospace Studies Rept. No. 113, (1966). (19) Milne, Τ. Α., Midwest Res. Inst. Rept. FS-127-P (1966). (20) Milne, Τ. Α., Greene, F. T.,J.Chem. Phys. 44, 2444 (1966). (21) Milne, Τ. Α., Greene, F. T., J. Chem. Phys., 47, 4095 (1967). (22) Milne, Τ. Α., Greene, F. T., Symp. Combust., 10th, p. 153, The Com bustion Institute, 1965. (23) Morton, H. S., Jr., Hagena, O. F., "Analysis of Intensity and Speed Dis tribution of a Molecular Beam from a Nozzle Source," Tech. Rept. UVA11-P, Contract No. Nonr 3623(00), October 1966. (24) Robben, F., Talbot, L., Phys. of Fluids 9, 644 (1966). (25) Scott, J., Phipps, J. Α., "Rarefied Gas Dynamics," Vol. 2, p. 1337, C. L. Brundin, ed., Academic Press, New York, 1967. (26) Sherman, F. S., Phys. of Fluids 8, 773 (1965). (27) Stern, S. Α., Waterman, P. C., Sinclair, T. F., J. Chem. Phys. 33, 805 (1960). (28) Taylor, W. J.,J.Chem. Phys. 38, 779 (1963). (29) Wilson, W. E., Jr., Symp. Combust., 10th, p. 47 (1965). RECEIVED November 2, 1966.
Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.