The vapor systems GeI2 and I2 and solid GeI4 were analyzed, using Raman spectroscopic techniques. The Raman bands of I2 and GeI4 were confirmed and Raman bands for GeI2 at 230 and 360 cm to the -1 power were reported. The application of the Raman techniques as a temperature probe in vapor transport kinetics was studied, and its feasibility is considered to be very good

Mcnutt, R. C.

Welsh 

NASA Technical Reports Server

NASA CR-144025 
Ad,d coct,,, 
ATHENS, ALABAMA 3561 1 
September 26 ,  1975 
(NASA-Ch- 144025)  S C L I U A F I C I T I O C  KIIJEIICS 
(Atheos C a l l . ,  k l a . )  1.3 & I ~ C  $3.51) CSCL 07C 
Unclas  
G 3 / 2 5  03034 
Nation?--: A e r o n a u t i c s  and Space A d m i n i s t r a t i o n  
George C .  M a r r h a l l  Space F l i g h t  Cen t e r  
M a r s h a l l  Space F l i g h t  C e n t e r ,  Alabn.ma 35812 
Submi t t ed  h e r e w i t h  i s  t h e  F i n a l  Repor t  on C o n t r a c t  NAs8-30561 w i t h  
Athens C o l l e g e ,  " ~ o l i d i f i c a t i o n  K i n e t i c s t 1 .  p r i n c i p & l  I n v e s t i g a t o r ,  
D r .  Ronald C .  McNutt. 
D i s t r i b u t i o n :  
A & PS-PR-RS 
Athens Co l l ege  B u s i n e s s  O f f i c e  
OI?R Res iden t  R e p r e s e n t a t i v e  
Research  I n s t i t u t e  
U n i v e r s i t y  of  Alabama, H u n t s v i l l e  
P o s t  O f f i c e  Box 1247 
H u n t s v i l l e ,  Alabama 35807 
c o v e r  l e t t e r  c n l y  
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5 c o p i e s  
9 c o p i e s  
cove r  l e t t e r  o n l y  , 
https://ntrs.nasa.gov/search.jsp?R=19760004172 2020-03-22T19:08:12+00:00Z
I n t r o d u c t i o n  
The p o t e n t i a l  advan t ages  i n  which m i c r o - g r a v i t y  environments  
1 h o l d s  f o r  manufac tu r ing  p r o c e s s e s  ha s  c r e a t e d  t h e  need t o  b e t t e r  d e f i n e  
some o f  t h e s e  p r o c e s s e s .  A good example i s  shown i n  t h e  e x c e l l e n t  
work of  D r .  H e r i b e r t  Wiedemeir of  R e n s s e l a e r  P o l y t e c h n i c  I n s t i t u t e .  1 
I n  h i s  vapor  t r a n s p o r t  e x p e r i m e n t s ,  t h e  z e r o  g r a v i t y  r e s u l t s  a lways 
gave h i g h e r  t r a n s p o r t  r a t e s  t h a n  t h e  t h e o r e t i c a l l y  p r e d i c t e d  r a t e s .  
Needless  t o  s a y  t h e r e  i s  a  s u b s t a n t i a l  need t o  u n d e r s t a n d  c e r t a i n  
p r o c e s s e s  b e t t e r  i f  we a r e  t o  u t i l i z e  them t o  t h e i r  p o t e n t i a l .  
T h i s  work was i n t e n d e d  t o  improve upon t h e  b a s i c  u n d e r s t a n d i n g  
P o f  such p r o c e s s e s  and t o  demons t r a t e  t h e  a b i l i t y  t o  make measure- 
, 
i '  ments i n  s i t u  f o r  t h e  vapor  t r a n s p o r t  p r o c e s s .  I n  o r d e r  t o  a c h i e v e  
t 
L 
t t h e s e  g o a l s ,  we c o n s i d e r e d  t h e  Raman t e c h n i q u e  as a  p o t e n t i a l  i n  
s P t u  p robe .  Due t o  t h e  t e c h n o l o g i c a l  advances  i n  t h e  l a s e r  i n d u s t r y ,  
h i g h  i n t e n s i t y  s o u r c e s  a r e  r e a d i l y  o b t a i n a b l e  and Raman s p e c t r o s c o p y  
I h a s  become a  v e r y  u s e f u l  a n a l y t i c a l  t o o l .  E x c e l l e n t  t e x t s  on Raman 
1 s p e c t r o s c o p y  and i t s  a p p l i c a t i o n  a r e  a v a i l a b l e .  2,3 Very l i t t l e  
t h e o r y  i s  g iven  i n  t h i s  r e p o r t .  We have i n t e n d e d  o n l y  t o  p r o v i d e  a  
f o u n d a t i o n  f o r  t h e  t y p e s  o f  measurements which can  b e  made w i t h  
t h e  Raman t e c h n i q u e ,  
T e c h n i c a l  Approach 
Raman s p e c t r o s c o p y  i s  an a l t e r n a t e  approach t o  v i b r a t i o n a l  
s p e c t r o s c o p y . w h i c h  h a s  become e x t r e m e l y  p o p u l a r  s i n c e  t h e  l a s e r  
ha s  become a v a i l a b l e  t o  s c i e n t i f i c  l a b o r a t o r i e s .  The a b i l i t y  t o  
per form m o l e c u l a r  i d e n t i f i c a t i o n s ,  e o n c e n t r a t i o n  m o n i t o r i n g ,  s t r u c t u r e  
a n a l y s i s  and t e m p e r a t u r e  measurements.  The Raman e f f e c t  a r i s e s  when 
an e l e c t r o m a g n e t i c  f i e l d  i n t e r a c t s  w i t h  an o s c i , l l a t * i n g  v i b r a t i o n  
w i t h i n  a mo lecu l e .  Th i s  i n t e r a c t i o n  i s  coup led  t h r o u g h  t h e  c o n f i g -  
u r a t i o n a l  changes  i n  t h e  n u c l e a r  and e l e c t r o n i c  p o s i t i o n s ,  o r  t h e  
p o l a r i z a b i l i t y  of  t h e  molecule .  For  t h e  Raman e f f e c t  t o  b e  an 
a l l owed  e f f e c t ,  t h e  mo lecu l a r  p o l a r i z a b i l i t y  must v a r y  w i t h  t h e  v i b r a t -  
i o n a l  mot ion o f  t h e  molecu le .  When t h e  above c o n d i t i o n  i s  s a t i s f i e d  
and t h e  mo lecu l e  i s  i r r a d i a t e d  w i t h  monochromatic l i g h t  of  f r equency  
f i  , t h e n  l i g h t  o f  frequencies&+!, and&-4is  e m i t t e d ,  where & i s  
a fundamenta l  v i b r a t i o n  o f  t h e  molecu le .  F i g u r e  1 i l l u s t r a t e s  t h i s  
s c h e m a t i c a l l y .  
S tokes  
Emiss ion 
F i g .  1 
By c o n v e n t i o n  t h e  l a t t e r  t e r m  i s  c a l l e d  S t o k e s  e m i s s i o n  and  
t h e  f o r m e r ,  a n t i - S t o k e s  e m i s s i o n .  The m a j o r  d i f f e r e n c e s  between 
i n f r a - r e d  and Haman t r a n s i t i o n s  a r e  d e t e r m i n e d  by  t h e  symmetry 
p r o p e r t i e s  0 9  t h e  m o l e c u l e s  and t h e  v i b r a t i o n s , % .  S i n c e  i n f r a -  
r e d  a b s o r p t i o n  depends  on a  change i n  t h e  d i p o l e  moment o f  t h e  
m o l e c u l e  w i t h  higl i  symmetry ( e . g .  O h ,  Td, o r  Dh p o i n t  g r o u p s )  
does  a l l o w  i n f r a - r e d  a b s o r p t i o n  f o r  t h e s e  v i b r a t i o n s .  However, 
t h e  p o l a r i z a b i l i t y  o f  t h e  molecu le  d o e s  change d u r i n g  t h e  
mot ion of  t h e  V i b r a t i o n  and  t h e s e  t r a n s i t i o n s  a r e  a l l o w e d  f o r  
t h e  Haman e f f e c t .  
In g e n e r a l  t h e  r u l e  s t a t e s  t h a t  m o l e c u l e s  which  h a v e  a  
c e n t e r  o f  symmetry,  t h o s e  v i b r a t i o n s  which p r e s e r v e  t h e  c e n t e r  ? : 
i < 
o f  symmetry c a n n o t  b e  i n f r a - r e d  a c t i v e ,  w h e r e a s  v i b r a t i o n s  which 
do n o t  p r e s e r v e  t h e  c e n t e r  of symmetry c a n n o t  b e  Raman a c t i v e ,  
. I f  b o t h  t h e  Raman a n d  t h e  i n f r a - r e d  s p e c t r a  a r e  o b s e r v e d  f o r  t h e  
same v i b r a t i o n ,  t h e n  we c a n  s a y  t h a t  t h e  m o l e c u l e  d o e s  n o t  have  
a  c e n t e r  o f  symmetry.  Germanium t e t r a i o d i d e  i s  a n  example o f  
t h e  f o r m e r  and germanium d i - i o d i d e  i s  an example o f  t h e  l a t t e r .  
F o r  GeI4,  t h e  A1 a n d  E v i b r a t i o n s  c a n  o n l y  b e  o b s e r v e d  w i t h  t h e  
Raman t e c h n i q u e ,  whereas  we can  o b s e r v e  t h e  F2 v i b r a t i o n s  w i t h  
e i t h e r  i n f r a - r e d  o r  Raman s i n c e  t h e s e  v i b r a t i o n s  t r a n s f o r m  as t h e  
x ,  y ,  z ,  x z ,  x y ,  a n d  y z  a x e s .  Hence we do have  a n  e x c e p t i o n  i n  t h e  
r u l e  f o r  t h i s  c a s e .  L i k e w i s e ,  a l l  t r a n s i t i o n s  f o r  Ge12 a r e  a l l o w e d  
i n  b o t h  t h e  i n f r a - r e d  and w i t h  Raman e x c i t a t i o n .  2 
. " 
S i n c e  t h e  Raman measurement i n v o l v e s  e x c i t a t i o n  f rom an i n t e n s e ,  
monochromat ic  l i g h t  s o u r c e  ( 8 a t i e f i e d  by l a s e r  s o u r c e s  i n  g e n e r a l ) ,  
, , 
t h e  amount of l i g h t  r e c e i v e d  b y  t h e  d e t e c t o r  s y s t e m  i s  d i r e c t l y  ' r '  . " 
. . 
. .. 
: > 
. I 
3 r. 
I ; 
., , 
I ,  
p r o p o r t i o n a l  t o  t h e  number o f  m o l e c u l e s  e x c i t e d  b y  t h e  l a s e r  s o u r c e .  
Hence t h i s  t e c h n i q u e  measures  c o n c e n t r a t i o n  d i r e c t l y  w i t h o u t  g o i n g  
t h r o u g h  Lambert-Beers t y p e  c a l i b r a t i o n s .  A l l  t h a t  i s  r e q u i r e d  i s  
t o  measure  t h e  Raman c r o s s - s e c t i o n  o r  c a l i b r a t e  a n  i n t e n s i t y  v e r s u s  
c o n c e n t r a t i o n  f o r  a  s p e c i f i c  power i n p u t  i n t o  t h e  ampoule i n  which  
t h e  measurement i s  t o  b e  made. S i n c e  v a p o r  t r a n s p o r t  e x p e r i m e n t s  
w i l l  b e  p e r f o r m e d  w i t h  t h e  o p t i c a l  s y s t e m  p a r a m e t e r e  p r e t t y  w e l l  
I c o n s t a n t ,  t h i s  t e c h n i q u e  s h o u l d  b e  v e r y  e f f e c t i v e  f o r  t h e s e  t y p e s  
I o f  e x p e r i m e n t s  - 
I Another  t e c h n i q u e  o r  measurement i n  which t h e  Raman e f f e c t  
I 
1 
! p r o v i d e s  a  c o n v e n i e n t  approach  i s  t h e  measurement o f  t e m p e r a t u r e  
i 
1 ,  i n  a g a s e o u s  sample .  A s  s e e n  i n  F i g .  1, t h e  m o l e c u l a r  s i g n a l s  
which w e  c a l l  S t o k e s  and  a n t i - S t o k e s  s i g n a l s  a r e  m e r e l y  t h e  
i 
d i f f e r e n c e s  i n  p o p u l a t i o n  o f  t h e  g round  v i b r a t i o n a l  l e v e l  r e l a t i v e  
t o  t h e  f i r s t  e x c i t e d  v i b r a t i o n a l  l e v e l .  Thus t h e  d i f f e r e n c e  i n  
p o p u l a t i o n  i s  g i v e n  by  t h e  Maxwell Boltzman d i s t r i b u t i o n ,  and t h e  
r a t i o  be tween  t h e  S t o k e s  and  t h e  a n t i - S t o k e s  s i g n a l s  i s  g i v e n  by: 
T (a.4; - s f o k s  ) 
C 
ku* 
- 
- -  
I ( stoker ) 
An example o f  t h i s  c a l c u l a t i o n  f o r  t h e  I2 s y s t e m  i s  g i v e n  i n  
T a b l e  I f o r  t h e  t e m p e r a t u r e  r a n g e  300-1000 d e g r e e s  K .  S i m i l a r  r a t i o s  
a r e  o b t a i n a b l e  f o r  GeI2 and GeI4. 
C o n c l u s i o n s  
I t  i s  e v i d e n t  f rom t h e  Raman e x p e r i m e n t s  p e r f o r m e d  on 1 2 ,  Ge12, 
and GeI4 t h a t  t h e  Raman t e c h n i q u e  i s  an e x c e l l e n t  p r o b e  f o r  m o l e c u l a r  
and t e m p e r a t u r e  p a r a m e t e r s  i n  v a p o r  t r a n s p o r t  e x p e r i m e n t s .  Us ing  an  
a r g o n  i o n  l a s e r  o f  1 t o  2 w a t t s  power ,  a number o f  d i f f e r e n t  t y p e s  
of  i n f o r m a t i o n  can  b e  o b t a i n e d  i n c l u d i n g  m o l e c u l a r .  i d e n t i f i c a t i o n ,  
c o n c e n t r a t i o n  and t e m p e r a t u r e  p r o f i l e s .  
I t  i s  s u g g e s t e d  t h a t  more a p p l i c a t i o n s  o f  l a s e r  p h y s i c s  t o  
v a p o r  t r a n s p o r t  k i n e t i c s  b e  c o n s i d e r e d  t o  improve t h e  d e p t h  o f  
knowledge f o r  t h e s e  p r o c e s s e s .  
Summary 
The v a p o r  s y s t e m s  GeI2 and I2 and s o l i d  GeI4 h a v e  b e e n  a n a l y z e d  
u s i n g  Raman s p e c t r o s c o p i c  t e c h n i q u e s .  The Raman b a n d s  o f  1 2  and  G e l k  
have  b e e n  c o n f i r m e d  and  Raman bands  f o r  GeI2 a t  230 cm-1 and  360 cm-1 
have  b e e n  r e p o r t e d  f o r  t h e  f i r s t  t i m e .  The a p p l i c a t i o n  o f  t h  Raman 
t e c h 3 i q u e  as a t e m p e r a t u r e  p r o b e  i n  v a p o r  t r a n s p o r t  k i n e t i c s  h a s  
been  s t u d i e d  a n d  i t s  f e a s i b i l i t y  i s  c o n s i d e r e d  t o  be v e r y  good. 
Acknowledgements a r e  t o  D r .  Gary L. Workman and  Mike Lenox 
f o r  a s s i s t a n c e  on t h i s  p r o j e c t .  
R . C .  McNutt t' 
P r i n c i p a l  I n v e s t i g a t o r  
TABLE I 
I ( a n t i - s t o k e s )  
Ratio for  I ( s t o k e s )  
E x p e r i m e n t a l  R e s u l t s  
The Raman s p e c t r a  which have  b e e n  o b s e r v e d  f o r  GeI4 s o l i d ,  
Ge12 v a p o r  and I2 a r e  g i v e n  i n  F i g .  2-4. A l s o  a s :ec t rophotomect-  
r i c  s c a n  f o r  I2 d i s s o l v e d  i n  c a r b o n  t e t r a c h l o r i d e  i s  shown i n  F i g .  5 .  
B o t e  t h a t  r a d i a t i o n  i s  a b s o r b e d  much more e f f i c i e n t l y  a t  514.5 nm 
t h a n  a t  488.0 nm, T h i s  l e a d s  t o  t h e  l a r g e  number o f  f l u o r e s e n c e  
b a n d s  f o r  1 2  as g i v e n  i n  F i g .  2 .  
A l l  Raman s p e c t r a  were  o b t a i n e d  w i t h  a  m o d i f i e d  Cary 81 Raman 
C 
S p e c t r o p h o t o m e t e r .  I t  was o r i g i n a l l y  b u i l t  f o r  T o r o n t o  a r c  
1 e x c i t a t i o n ,  b u t  o u r  work r e q u i r e d  l a s e r  e x c i t a t i o n .  A l l  t h e  T o r o n t o  
i a r c  a p p a r a t u s  was s u b s e q u e n t l y  removed and t h e  beam from a  S p e c t r a -  
P h y s i c s  Model 1 6 4  Argon I o n  L a s e r  was d i r e c t e d  i n t o  t h e  s a m p l i n g  
volume.  We d i d  h a v e  a  number o f  p rob lems  i n  o b t a i n i n g  h i g h  q u a l i t y  
s p e c t r a  o r i g i n a l l y  b e c a u s e  o f  t h e  o p t i c a l  t r a i n  d e s i g n e d  f o r  
T o r o n t o  a r c  e x c i t a t i o n .  
I 
i 
! 
i We were  a b l e  t o  o p t i m i z e  t h e  Raman s i g n a l s  a f t e r  some manipu la -  
i 
f t i o n  o f  s a m p l i n g  g e o m e t r y .  A c o m p i l a t i o n  o f  o u r  r e s u l t s  i s  g i v e n  
I 
I 
1 i n  T a b l e  11. We were  u n a b l e  t o  f i n d  any p r e v i o u s  d a t a  on GeI2,  s o  
1 o u r  r e s u l t s  a r e  t h e  f i r s t  f o r  t h i s  s p e c i e s .  



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B i b l i o g r a p h y  
1 .  H .  Wiederneir,  "Growth o f  S i n g l e  C r y s t a l s  by  Vapor Transpor t  i n  
Zero G r a v i t y  ~ n v i r o n m e n t "  C o n t r a c t  N A S ~ - 2 6 1 4 6 .  
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Solidification kinetics

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