Oxygen and carbon dioxide UV photolysis studied with resonance fluorescence to analyze planetary atmospheric processe

Slanger, T. G.

English

NASA Technical Reports Server

February 10 ,  1970 
Semiannual Report 
For t h e  Per iod  J u l y  15 ,  1969 t o  January 15 ,  1970 
LABORATORY CO, PHOTOLYSIS STUDIES RELATED TO PLANETARY ATMOSPHERES 
By: Tom G .  S langer  
Prepared for: 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
Washington, D . C .  20546 
Attn:  Chief P l a n e t a r y  Atmospheres, Code SL 
SRI P r o j e c t  No. PAU-8162 NASA C o n t r a c t  No. NSR 05-019-252 
Approved: 
F e l i x  T .  Smith, Manager 
Molecular Phys ics  
E .  M .  Kinderman, D i r e c t o r  
Phys ica l  Sciences 
Copy No. 
https://ntrs.nasa.gov/search.jsp?R=19700010421 2020-03-12T00:59:37+00:00Z
Introduction 
This work under NASA sponsorship (Contract No. NSR 05-019-252) was 
undertaken to increase our understanding of the details of CO, uv photol- 
ysis processes, including determination of the initial dissociation 
products, and the paths and rates of the subsequent secondary reactions. 
Monitoring of the O(3P> concentration by means of resonance fluorescence 
was chosen as a desirable method of achieving these ends, because of the 
minimum perturbation induced in the system by such a technique. We hope 
results will clarify the processes taking place in the Mars and Venus 
atmospheres; a secondary benefit is that development of an effective 
O ( 3 P )  resonance lamp can be useful in measurements of O(3P> concentrations 
in planetary atmospheres, including that of the earth. 
Achievements 
During the first six months efforts, reported here, a primary ob- 
jective has been to construct a lamp emitting the 01 1302-1306 A reso- 
nance triplet with sufficient intensity at the line centers to make res- 
onance fluorescence measurements of O(3P> atom concentrations produced 
in 0,  and CO, photolysis practical. This has been accomplished. The 
lamp is a flowing microwave discharge of 1% 0, in Ar, with a MgF, window; 
at present, experiments carried out with 0, as the 0 atom source give sig- 
nal to noise ratios on the order of 500. The original lamp design was 
not ideal because a considerable amount of the resonance light emitted 
was reversed, and therefore could not be absorbed by O ( 3 P > .  
sulted in the signal due to scattered light from the walls being approxi- 
mately equal to the fluorescence signal. Although such a situation does 
not present a serious problem, a new lamp has been constructed that 
greatly increases the absorbable light and increases detection sensitiv- 
ity for O( 3 ~ >  atoms. 
0 
This re- 
Experiments with 0, and CO, photolysis have been underway for  two 
months and some interesting observations have been made, although it must 
be stressed that the findings are preliminary and subject to reinterpre- 
tation. Results to date are as follows: 
L 
_. . 
,- 
1. The measurement of t h e  O(,P) produced from CO, p h o t o l y s i s  shows, 
when compared t o  resu l t s  from 0, p h o t o l y s i s ,  t h a t  O(,P) i s  pro- 
duced wi th  a quantum y i e l d  of 1 . 0 .  T h i s  means t h a t  i f  CO, i s  
formed as a s t e p  i n  t h e  O('D) d e a c t i v a t i o n  [O('D) i s  t h e  i n i t i a l  
CO, d i s s o c i a t i o n  product] by a r e a c t i o n  CO, + O('D) + CO,, t h e  
CO, must t hen  d.ecompose t o  O(3P)  + CO, b e f o r e  any of i t  l e a v e s  
t h e  sys t em,  i . e . ,  w i t h i n  0 . 2 5  seconds. 
2 .  When H, i s  added t o  CO, dur ing  p h o t o l y s i s  of t h e  l a t t e r ,  i t  re- 
moves t h e  O('D) without  a f f e c t i n g  t h e  O(,P), and i t  does so  a t  
a ra te  comparable t o  t h e  r a t e  a t  which CO, d e a c t i v a t e s  O('D) t o  
O(,P), as our prev ious  work i n d i c a t e d .  Th i s  i s  most impor tan t ,  
because t h e  c rux  of t h e  argument over  CO, p h o t o l y s i s  is  whether 
O('D) i s  d e a c t i v a t e d  by CO, a t  t h e  r a p i d  ra te  p rev ious ly  mea- 
su red  by us ,  or a t  t h e  r a t e  100 times s lower  measured by Noxon. 
A s  t h i n g s  now s t a n d ,  w e  can r a t i o n a l i z e  Noxon's d a t a  by assuming 
t h a t  our  f a s t  r a t e  is  c o r r e c t ,  and t h a t  h i s  data  invo lves  CO,. 
On t h e  o t h e r  hand, w e  can f i n d  no exp lana t ion  f o r  our r e s u l t s ,  
now t w i c e  demonstrated by e n t i r e l y  d i f f e r e n t  methods, and re- 
c e n t l y  confirmed by Paraskevopoulos and Cvetanovik, t i f  Noxon's 
slow ra te  is  c o r r e c t .  
* 
3: Measurements of t h e  l o s s  rates of O(3P) i n  our flow system have 
been made i n  t h e  presence  of CO, and 0,, and t h e r e  i s  no s i g n i f i -  
c a n t  d i f f e r e n c e  between them. I n  both  cases, t h e  l o s s  i s  gov- 
e rned  by t h e  pumpout  t i m e  of t h e  system. Th i s  means t h a t  d i f -  
f e r i n g  O(,P> concen t r a t ions  measured i n  t h e  two i n s t a n c e s  w i l l  
r e f l e c t  t h e  p roduc t ion  r a t e  of O(,P), and n o t  t h e  l o s s  rates,  
a n  impor tan t  p o i n t  i n  i n t e r p r e t i n g  t h e  d a t a .  
2% 
" J. F. Noxon, Can. J. Chem. 47, 1873 (1969).  -
G .  Paraskevopoulos and R .  J. Cvetanovih, J. Am. Chem. SOC. 91:27, 
7572 (1969) .  
2 
When this project was started, it was first necessary to carry out some 
studies of CO resonance fluorescence, as this subject has a bearing on 
our observations. The results of a part of this work are soon to be 
published in Chemical Physics Letters under the title "The Perturbation 
Spectrum of CO." 
fluorescence processes involving forbidden electronic transitions, which 
take place because of intramolecular perturbation effects. A copy of 
the paper has already been forwarded to NASA. 
The paper describes observations on forced resonance 
Plans for Completion of Project 
A s  stated above, a new lamp has been designed which will improve 
the system considerably. Further experiments are planned with 0,, CO,, 
and combinations thereof, to confirm the observations made so far. The 
effect of CO addition will also be investigated, as its behaviour has 
been previously found to be somewhat anomalous. With reference to CO,, 
various tests will be devised to search for concrete evidence f o r  this 
species. Experiments will be carried out with a pulsed Xe lamp in order 
to determine if there is any time lag between the start of a pulse and 
the appearance of O( ,P) .  
the lifetime of a CO, intermediate. A s  yet, our results do not require 
any hypothesis involving CO,; it is needed only to reconcile Noxon's 
results with ours. 
Such experiments will set an upper limit on 
3 


Laboratory CO2 photolysis studies related to planetary atmospheres Semiannual report, 15 Jul. 1969 - 15 Jan. 1970

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