On the exponential energy gap law in He--I sub 2 vibrational relaxation

Journal Article · Wed Aug 15 04:00:00 EDT 1990 · Journal of Chemical Physics; (USA)

DOI:https://doi.org/10.1063/1.459026· OSTI ID:6513569

Maricq, M M ^[1]

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1. Research Staff, Ford Motor Company, P.O. Box 2053, Drop 3083, Dearborn, Michigan 48121 (USA)

A comparison between coupled states, infinite order sudden, and classical path calculations is used to elucidate the origin of an exponential energy gap law recently observed for vibrational relaxation from highly excited states in the {ital B} 0{sup +}{sub {ital u}} state of I{sub 2} due to collisions with He. All three methods provide relaxation cross sections in good agreement with experiment. Anharmonic effects play an important role, with accurate results obtained with a Morse, but not harmonic, oscillator description of the I{sup *}{sub 2} molecule. The nearly exact agreement between rotationally summed coupled states cross sections and the IOSA is consistent with the view that the I{sup *}{sub 2} molecule does not rotate significantly during a collision. A closed form solution of the forced harmonic oscillator, valid for highly excited states, predicts a {ital J}{sup 2}{sub {vert bar}{Delta}{ital v}{vert bar}} distribution of vibrationally relaxed states at a given collision angle and impact parameter. The vibrationally close coupled-infinite order sudden (VCC-IOSA) results bear this out and show that the observed exponential scaling law arises from a superposition of such distributions over {theta} and {ital b}.

• OSTI ID: 6513569
• Journal Information: Journal of Chemical Physics; (USA), Journal Name: Journal of Chemical Physics; (USA) Vol. 93:4; ISSN JCPSA; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
BEAMS
COLLISIONS
CROSS SECTIONS
ELEMENTS
ENERGY GAP
ENERGY LEVELS
EXCITED STATES
FLUIDS
GASES
HALOGENS
HELIUM
IODINE
MOLECULAR BEAMS
MOLECULE COLLISIONS
NONMETALS
RARE GASES
RELAXATION
SUDDEN APPROXIMATION
VIBRATIONAL STATES