Counting vibrational quanta with a diode laser probe: Bending and stretching excitation in CO/sub 2/ caused by collisions with hot atoms from excimer laser photolysis
A high resolution (10/sup -3/ cm/sup -1/) cw diode laser probe technique has been developed and used to determine the number of CO/sub 2/ vibrational quanta of each kind (..nu../sub 3/ antisymmetric stretch, ..nu../sub 2/ bend, and ..nu../sub 1/ symmetric stretch) produced as a result of collisions between translationally hot hydrogen atoms and CO/sub 2/ molecules. The experimental method relies on probes of the CO/sub 2/ vibrational transitions mn/sup l/p ..-->.. mn/sup l/( p+1) all of which ''ride'' the large oscillator strength of the fundamental 00/sup 0/0 ..-->.. 00/sup 0/1 antisymmetric stretching transition. Transitions with different values of m, n, l, and p are easily separated due to the narrow spectral characteristics of the diode laser and the small anharmonicities associated with different vibrational quantum numbers. The probability for excitation of a CO/sub 2/ ..nu../sub 3/ quantum by collisions with hot hydrogen atoms produced by 193 nm excimer laser photolysis of H/sub 2/S is about 1% per gas kinetic collision. Bending (..nu../sub 2/) quanta are produced about 5--6 times more efficiently than (..nu../sub 3/) antisymmetric stretching quanta. A precise value for the excitation probability of symmetric stretching (..nu../sub 1/) quanta cannot be obtained due to rapid equilibration between ..nu../sub 1/ and 2..nu../sub 2/, but the number of ..nu../sub 1/ quanta is found to be roughly one third the number of ..nu../sub 3/ quanta. The thermalization rate for cooling hot hydrogen atoms below threshold for excitation of a CO/sub 2/ ..nu../sub 3/ quantum corresponds to two H atom/H/sub 2/S collisions or 16 H atom/CO/sub 2/ collisions.
- Research Organization:
- Department of Chemistry and Columbia Radiation Laboratory, Columbia University, New York, New York 10027
- DOE Contract Number:
- AC02-78ER04940
- OSTI ID:
- 6162868
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 81:12; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
ATOMS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
COLLISIONS
DECOMPOSITION
ELEMENTS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXCITED STATES
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
LASER SPECTROSCOPY
MOLECULE COLLISIONS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
SPECTROSCOPY
SULFIDES
SULFUR COMPOUNDS
VIBRATIONAL STATES