Rotational and Vibrational Excitation of CO Molecules by Collisions with⁴He Atoms

Abstract

Full close-coupled calculations are carried out of the cross sections for energy transfer between rotational levels of carbon monoxide in collision with 4 He atoms with energies between 5 and 600 cm À1. At low energies, the cross sections are dominated by contributions from shape resonances. The calculated cross sections are in satisfactory agreement with the experimental data measured at an energy of 570 cm À1. Calculations using the infinite order sudden approximation are carried out of cross sections for energy transfer between vibrational levels of CO. Vibrational energy transfer is dominated by transitions in which the vibrational quantum number changes by unity.

Ro-vibrational quenching of CO (v = 1) by He impact in a broad range of temperatures: A benchmark study using mixed quantum/classical inelastic scattering theory

“…For example, cross section for a transition from the initial ro-vibrational state (v, j ) into the final state (v , j ) at collision energy E is denoted by σ jj vv (E). Quantum mechanical expression for the rate coefficient of vibrational quenching from v = 1 into v = 0 is [15][16][17]19 κ dir 10 (T ) = 8kT μπ…”

“…6,7 It has been studied in the past both theoretically [8][9][10][11][12][13][14][15][16][17][18][19] and experimentally 3,18 in a broad range of temperatures. For example, rotational-vibrational transitions of CO is a valuable diagnostic probe of diverse astrophysical environments, such as interstellar and circumstellar media, [20][21][22][23][24] where the temperatures of interest are very high, up to T ∼ 2500 K. Rovibrational transitions in the intermediate temperature range, 300 K < T < 1000 K, are important to the post-combustion kinetics of CO. [23][24][25] Finally, these processes play critical role in developing the methods for cooling (and trapping) molecules to (at) sub-Kelvin temperatures, because efficiency of experimental techniques depends on the ratio between elastic and inelastic scattering cross sections.…”

“…Another set of data is from the "reverse" approach, where cross sections for excitations from v = 0 to v = 1 are computed first, and then converted into the quenching rates using the principle of microscopic reversibility. 19,44 One more set of data is from the average-velocity (symmetrized) approach of Billing, 45 where the principle of microscopic reversibility is built in by construction, and the results of direct and reverse calculations are very similar to each other.…”

Equivalence of the Ehrenfest theorem and the fluid-rotor model for mixed quantum/classical theory of collisional energy transfer

“…The result of such collision is usually a nonreactive inelastic scattering process, but dissociation of the molecule and/or the quencher may also occur. In some applications, the focus is on quenching of the low-lying internal states of the molecule (e.g., few quanta of ro-vibrational excitation [2][3][4][5][6][7][8] ) while in other processes, such as recombination reactions, [9][10][11][12][13] the molecule is initially at energy above the dissociation threshold (scattering resonance). Several processes that are reverse to quenching, such as collisional excitation and the collision-induced dissociation, also fall into the category of the collisional energy transfer.…”

Uncertainties in water chemistry in disks: An application to TW Hydrae

“…(1) Jaquet et al (1992); (2) Abrahamsson et al (2007); (3) Schöier et al (2005); (4) Bell et al (1998); (5) Wilson & Bell (2002); (6) Hammami et al (2009);Turpin et al (2010), rates for He scaled by 1.39; (7) Lim et al (1999); (8) Flower (1999); (9) Yang et al (2010); (10) Balakrishnan et al (2002); (11) Cecchi-Pestellini et al (2002); (12) Offer et al (1994); (13) Green (1980); (14) Faure & Josselin (2008).…”