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Title: On the validity of collider-mass scaling for molecular rotational excitation

Rate coefficients for collisional processes such as rotational and vibrational excitation are essential inputs in many astrophysical models. When rate coefficients are unknown, they are often estimated using known values from other systems. The most common example is to use He-collider rate coefficients to estimate values for other colliders, typically H{sub 2}, using scaling arguments based on the reduced mass of the collision system. This procedure is often justified by the assumption that the inelastic cross section is independent of the collider. Here we explore the validity of this approach focusing on rotational inelastic transitions for collisions of H, para-H{sub 2}, {sup 3}He, and {sup 4}He with CO in its vibrational ground state. We compare rate coefficients obtained via explicit calculations to those deduced by standard reduced-mass scaling. Not surprisingly, inelastic cross sections and rate coefficients are found to depend sensitively on both the reduced mass and the interaction potential energy surface. We demonstrate that standard reduced-mass scaling is not valid on physical and mathematical grounds, and as a consequence, the common approach of multiplying a rate coefficient for a molecule-He collision system by the constant factor of ∼1.4 to estimate the rate coefficient for para-H{sub 2} collisions is deemedmore » unreliable. Furthermore, we test an alternative analytic scaling approach based on the strength of the interaction potential and the reduced mass of the collision systems. Any scaling approach, however, may be problematic when low-energy resonances are present; explicit calculations or measurements of rate coefficients are to be preferred.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Department of Physics and Astronomy and Center for Simulational Physics, The University of Georgia, Athens, GA 30602 (United States)
  2. Department of Chemistry, University of Nevada, Las Vegas, NV 89154 (United States)
  3. Department of Physics, Pennsylvania State University, Berks Campus, Reading, PA 19610 (United States)
Publication Date:
OSTI Identifier:
22365526
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; CARBON MONOXIDE; COLLISIONS; COMPARATIVE EVALUATIONS; CROSS SECTIONS; ELECTRIC GROUNDS; EXCITATION; GROUND STATES; HELIUM 3; HELIUM 4; HYDROGEN; INTERACTIONS; MASS; MOLECULES; SCALING; SCATTERING