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Title: Theoretical investigation of intersystem crossing between the a{sup ~1}A{sub 1} and Χ{sup ~3}B{sub 1} states of CH{sub 2} induced by collisions with helium

Collisional energy transfer between the ground (Χ{sup ~3}B{sub 1}) and first excited (a{sup ~1}A{sub 1}) states of CH{sub 2} is facilitated by strong mixing of the rare pairs of accidentally degenerate rotational levels in the ground vibrational manifold of the a{sup ~} state and the (020) and (030) excited bending vibrational manifolds of the X{sup ~} state. The simplest model for this process involves coherent mixing of the scattering T-matrix elements associated with collisional transitions within the unmixed a{sup ~} and X{sup ~} states. From previous calculations in our group, we have determined cross sections and room-temperature rate constants for intersystem crossing of CH{sub 2} by collision with He. These are used in simulations of the time dependence of the energy flow, both within and between the X{sup ~} and a{sup ~} vibronic manifolds. Relaxation proceeds through three steps: (a) rapid equilibration of the two mixed-pair levels, (b) fast relaxation within the a{sup ~} state, and (c) slower relaxation among the levels of the X{sup ~} state. Collisional transfer between the fine-structure levels of the triplet (X{sup ~}) state is very slow.
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021 (United States)
  2. Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021 (United States)
  3. Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685 (United States)
Publication Date:
OSTI Identifier:
22420029
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COLLISIONS; CROSS SECTIONS; ENERGY TRANSFER; FINE STRUCTURE; HELIUM; REACTION KINETICS; RELAXATION; SCATTERING; SIMULATION; TIME DEPENDENCE