The photoabsorption and photodissociation cross sections of several interstellar molecules and radicals in the 105 to 210 nm region were measured. The research results accomplished are briefly described. Photoabsorption cross sections of OD and CN, and photoabsorption and photodissociation of HCl, and photoabsorption and photodissociation cross sections of CH3OH are discussed

Lee, L. C.

English

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F
(NASA-CB-175918) PR070ADSORP7I011 AND
PHOTODISSOCIATICH OF MOLECULES IMPORTANT IN
THE INTERSTELLAR MEDIUM Annual Report, '15
May 1984 "14 Hay 1965 (San Diego State
Uuiv- , Calif.) 8 p HC A02/ME A01
	 CSCL 03B G3/90
N85-30986
Unclas
21561
:uly 1, 1985
Annual Report for Gran No. NAC10319
covering period fr	 5 May 1984 to 14 May 1985
Photoabsorption and Photodissociation of Molecules Important in
the Insterstellar Medium
By:
Long C. Lee
Department of Electrical and Computer Engineering
San Diego State University
San Diego, California 92182-0190
Telephone: (619) 265-3701
Prepared for:
National Aeronautics and Space Administration
NASA Headquarters
Washington, D. C. 20546
Attention: Dr. Robert E. Stencel
Astrophysics Division, Code E2-7
Endorsed by:
Dr. Long C. Lee
Professor
Electrical and Computer Engineering
1
TABLE OF CONTENTS
Page
	
I.	 INTRODUCTION ..............................................3
	
II.	 RESEARCH ACCOMPLISHED .....................................3
A. Photoabsorption Cross	 Section	 of	 OD ...................3
B. Photoabsorption Cross	 Section	 of	 CN ...................3 i
C. Photoabsorption and Photodissociation of HC1 .......... 4
D. Photoabsorption and Photodissociation of CH30H ........ 5
III. PUBLICATIONS AND PRESENTATIONS RESULTING FROM THIS
RESEARCHPROGRAM ..........................................5
VI	 APPENDICES	 u
A: Photoabsorption Cross Section of OD at 115-180 nm
B: Photodissociation Rates of OH, OD and CN by the
Interstellar Radiation Field
C: Quantitative Studies for Photoabsorption 	 and
Fluorescence of HC1
D: Photoexcitation Processes of CH30H: Rydberg States
and Photofragment Fluorescence
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I. INTRODUCTION
This report describes the results obtained in the period
from May 15, 1984 to May 14, 1985 for the research program
supported by NASA under Grant No. NAGW-319. This research
program is to measure the photoabsorption and photodissociation
cross sections of molecu les and radicals important in the
interstellar medium. These data are currently needed for
understanding the formation and destruction processes of these
molecules and radicals in the interstellar medium.
II. RESEARCH ACCOMPLISHED
In this research program, we have measured the
photoabsorption and photodissociation cross sections of several
interstellar molecules and radicals in the 105-210 nm .region.
The research results accomplished during this funding period are
briefly described below.
A. Photoabsorotion Cross Section of OD
The OD radical is very similar to the most abundant
interstellar radical OH in both physical and chemical nature.
The photodissociation rate of OD by the interstellar radiation
field is thus interested in understanding the isctope effect of
the interstellar chemistry. We have measured the photoabsorption
cross sections of OD in the 115-180 nm region in the current
funding period. The results are summarized in a paper published
it the Journal of Chemical Physics which is attached as Appendix
A.
The photoabsorption cross sections are used to calculate the
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Tphotodissociation rate of OD by the interstellar radiation field.
The results are summarized in a paper published in
	
the
-	 Astrophysical Journal that is attached as Appendix B.
S. Photoabsorption Cross Section of CK
The CN radical is quite abundant in the interstellar medium,
4
whose destruction is mainly through the photodissociation
process.	 We have investigated the photoabsorption of CN in the
115-200 nm region in the current funding period. 	 The absorption
cross section is so small that only an upper limit
	 is
established.	 The upper limit for the photodissociation of CN by
the interstellar radiation field in the 115-190 nm region is
fib
raj. 2x10-10 s- 1 .	 This upper limit has been used by Dr. Steven
.lit Federman at the Jet PropuloJon Laboratory to confirm his analysis
^	 of field observation (private communication 1984). 	 Our results
are summarized in a paper attached as Appendix B.
C. Photoabsor ption and Photodissociation of HC1
The cross sections for the photoabsorption and fluorescence
of HC1 have been measured in the 105-200 nm region using
synchrotron radiation as a light source.	 The results are
summarized in a paper attached as Appendix C. In the present
results, we find that the absorption cross sections at the peaks
of some absorption bands are quite high so that the light source
intensity may be totally attenuated at the gas pressures we used.
This will make the measured photoabsorption cross sections appear
low.	 We will confirm the measurement in the next synchrotron
radiation experiment.
4
D. Photoabeorntion and Photodisaociatiian Cross Sections of CHaOH
The photoebsorption and fluorescence cross sections of
methanol vapor were measured in the 106-198 nm region. Weak
structures were observed in the 110-140 nm region and were
classified into three Rydberg series. The fluorescence cross
section was used to infer the photodissociation cross section
Of CH30H that is useful for calculating the photodissociation
rate of CH30H by the interstellar radiation field. This work has
i
been summarized in a paper attached as Appendix D, which is
accepted for publication in Chemical Physics.
	
III. Publications and Presentations Resulting from this Research 	 1
Program
	
The cumulative publications and presentations obtained from	 I'
this research program are listed as follows.
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PUBLICATIONS AND PRESENTATIONS RESULTING FROM THIS RESEARCH PROGRAM
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1. L. C. Lee, "Emissions from Photofragments of HCN", presented at the 178th
American Chemical Society Meeting, Washington, D. C., September 10-14, 1979.
2. L. C. Lee, "OH(A2E+ + X2Ri) Yield from H 2O Photodissociation in 1050-1370
J. Chem. Phys. 721, 4334 (1980).
3. L. C. Lee, "CN(A 211, + X 2 E + ) and CN(B 2E+ + X 2 E + ) Yields from HCN Photodisso-
ciation", J. Chem. Phys. 72, 6414 (1980).
4. L. C. Loc o, " Photodissociation of Interstellar Molecules, H 2O and HCN", pre-
sented at the 1979 Synchrotron Radiation Users Group Meeting, Madison, Wis-
consin, October 25-26, 1979.
5. L. C. Lee, "CN(A 2Hi , B 2 E + + X2E+) Yields from HCN Photodissociation", pre-
sented at the 14th Informal Conference on Photochemistry, Newport Beach,
California, March 30 - April 3, 1980.
6. L. C. Lee, "OH(A 2E+ + X2 Ili ) YieldF from 1120 Photodissociation", presented
at the VI International Conference on Vacuum Ultraviolet Radiation Physics,
Charlottesville, Virginia, June 2-6, 1980.
7. J. A. Guest and L. C. Lee, "Photoabsorption and Photodissociation of Inter-
stellar Molecules, NO", presented at the 1980 Annual Synchrotron Radiation
Users Group Meeting, Madison, Wisconsin, October 20-21, 1980.
S.
	
J. A. Guest and L.C. Lee, "Quantitative Absorption and Fluorescence Studies
of NO Between 1060-2000 A", J. Phys. B: Atom. Molec. Phys. 14- 3401 (1961);
Also presented at the Thirty-Sixth Symposium on Molecular Spectroscopy, Ohio
State University, Columbus, Ohio, June 15-19, 1981.
9. L. C. Lee andJ. A. G est, "Quantitative Absorption and Fluorescence Studies
of CO from 1060-1550 ^", J. Phys. B: Atom. Molec. Phys, 14, 415 (1981).
10. L. C. Lee and C. C. Chiang, "Fluorescence Yields from Photodissociation of
CH4% presented at the 1981 Annual Synchrotron Radiation Users Group Meeting,
Madison, Wisconsin, October 19-20, 1981.
11. L. C. Lee and C. C. Chiang, "Fluorescence Yields from Photodissociation of	 ;4
OCS at 1060-1240 X", Chem. Phys. Lett. 92, 425 (1982).
12. M. Suto, R. L. Day, and L. C. Lee, "Fluorescence Yields from Photodissociation
Of S02 at 1060-1330 a", J. Phys. B:At. Mol. Phys. 15, 4165 (1982); also pre-
sented at the International Symposium on Chemical Kinetics Related to Atmos-
pheric Chemistry, Tsukuba, Japan, June 6-10, 1982.	 i
13. R. L. Day, M. Suto, and L. C. Lee, Photodissociation Yields of C52 at 1060- ,
1520 ", J. Phys. B; At. Mol. Phys. 151' 4403 (1982).	 I`
14, M Suto, Raa L. Day, and L. C. Lee, "Photodissociation Processes of S02 at	 4
1060-1330 A", presented at the XV Informal Conference on Photochemistry,
Stanford, California, June 26 - July 1, 1982.
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15. R. L. Day, M. Suto, and L. C. Lee, "Photodisso.iation Processes of CS 2 at
1060-1520 a", presented at the XV Informal Conference on Photochemistry,
Stanford, California, June 26 - July 1, 2.982.
16. R. L. Day and L. C. Lee, "Photoabsorption Spectrum of OH in the Vacuum Ultra-
violet Region", presented at the XV Informal Conference on Photochemistry,
Stanford, California, June 26 - July 1, 1982.
17. M. Suto and L. C. Lee, "Fluorescence Yields from Photodissociation of NH3",
presented at the 15th Annual Synchrotron Radiation Users Group Meeting, Madi-
son, Wisconsin, October 18-19, 1982.
18. L. C. Lee and M. Suto, "Photodissociation Processes of NH3 at 106-220 rim",
presented at the Fall Meeting of American Geophysical Union, San Francisco,
California, December 7-15, 1982.
19. L. C. Lee and C. C. Chiang, "Fluorescence Yields from Photodissociation of
CH4 at 1060-1420 R", J. Chem. Phys. 78, 688 (1983).
20. M. Suto and L. C. Lee, "Photodissociation of NH3 at 106-200 nm", J. Chem.
Phys. 78, 4515 (1983).
21. R. L. Day, and L. C. Lee, "Photoabsorption Spectrum of Radicals Produced by
a Pulsed Discharge of Trace H2O in Ar", Chem. Phys. 75, 17 (1983).
22. M. Suto and L. C. Lee, "Photodissociation Processes of N20, HNO3, and C2H2",
presented at the 16th Annual Synchrotron Radiation Users Group Meeting, Madison,
Wisconsin, October 24-25, 1983.
23. L. C. Lee and M. Suto, "Photodissociation of C2H2", presented at the 1983 Fall
Meeting of the American Geophysical Union, San Francisco, California, Decem-
ber 4-9, 1983.
24. L. C. Lee, "Photodissociation Rates of Molecules by the Interstellar Radiation
Field", Astrophys. J., 282, 172 (1984).
25. M. Suto and L. C. Lee, "Quantitative Photoexcitation and Fluorescence Studies
of C 2 H 2 in Vacuum Ultraviolet", J. Chem. Phys., 80, 4824 (1984).
26. J. B. Nee and L. C. Lee, "Photoabsorption Cross Section of OH in Vacuum Ultra-
violet", J. Chem. Phys. 81, 31 (1984).
27. J. B. Nee and L. C. Lee, "Photoabsorption Cross Section of OD at 115-180 nm",
J. Chem. Phys. 81, 3811 (1984).
28. J. B. Nee, M. Suto and L. C. Lee, "Experimental Studies of the Photodissocia-
tion Processes of OH, OD, and CN" presented at the XVI Informal Conference
on Photochemistry, Harvard University, Boston, August 20-24, 1984.
29. J. B. Nee, M. Suto and L. C. Lee, "Photoexcitation Processes of HC1 and HBr
in !'UV", presented at the 1984 Synchrotron Radiation User's Meeting,
Madison, Wis., Oct. 22-23, 1984.
.x
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i30. J. B. Nee, M. Suto and L. C. Lee, "Photoabsorption and Photodissociation
of 11C1 and H8r in the Vacuum Ultraviolet Wavelengths" presented at the
1984 Fall Meeting, American Geophysical Union, San Francisco, Caltf.,
Dec. 3-7, 1984.
31. J. B. Nee and L. C. Lee, "Photodissociation Rates of OH, OD and CN
by Ehe Interstellar Radiation Field", Astrophys. J., 291, 202 (1985)
32. J. B. Nee, M. Suto, and L. C. Lee, "Photodissociation Processes
of Hydrogen Halides Studied with £ynchrotron Radiation", to be
presented at the XIV International Conference on the Physics of
Electronic and Atomic Collisions, Palo Alto, CA., July 24-30, 1985.
33. J. B. Nee and L. C. Lee, "Photoabsorption Cross Sections of Inter-
stellar Free Radicals in the Vacuum Ultraviolet Wavelengths", to be
presented at the 17th International Symposium on Free Radicals,
Granby, CO., Aug. 18-23, 1985
34. J. D. Nee, M. Suto and L. C. Lee, "Photoexcitation Processes of C113OH;
Rydberg States and Photofragment Fluorescence", Chemical Physics, in
press.
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Photoabsorption and photodissociation of molecules important in the interstellar medium

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