A close-coupling study of vibrational-rotational quenching of CO by collision with hydrogen atoms

Rotational energy transfer in the collision of N2O with He atom

The quantum state-to-state rotationally inelastic quenching of N2O by colliding with a He atom is studied on an ab initio potential energy surface with N2O lying on its vibrational ground state. The cross sections for collision energies from 10-6-100 cm-1 and rate constants from 10-5-10 K are calculated employing the fully converged quantum close-coupling method for the quenching of the j = 1-6 rotational states of N2O. Numerous van der Waals shapes or Feshbach resonances are observed; the cross sections of different channels are found to follow the Wigner scaling law in the cold threshold regime and may intersect with each other. In order to interpret the mechanism and estimate the cross sections of the rotational energy transfer, we propose a minimal classical model of collision between an asymmetric double-shell ellipsoid and a point particle. The classical model reproduces the quantum scattering results and points out the attractive interactions and the potential asymmetry can affect the collision process. The resulting insights are expected to expand our interpretations of inelastic scattering and energy transfer in molecular collisions.

Rotational quenching of CO2 by collision with He atoms

Quantum mechanical scattering calculations are presented for the rotational relaxation of CO(2) in collisions with He atoms with the close-coupling approach and the coupled-states approximation for collision energies between 10(-6) and 10 000 cm(-1). The He-CO(2) interaction potential of Ran and Xie [J. Chem. Phys. 128, 124323 (2008)] was adopted and used to compute state-to-state cross sections for the quenching of the j=2, 4, 6, and 8 rotational levels of CO(2). Numerous resonances, as a consequence of the van der Waals potential, are observed and the cross sections are found to approach the Wigner limit at low energies. Quenching rate coefficients are obtained for temperatures between 10(-5) and 3000 K and applications to astrophysics and cold collisions are briefly discussed.

Quenching of rotationally excited CO by collisions with H2

Quantum close-coupling and coupled-states approximation scattering calculations of rotational energy transfer in CO due to collisions with H2 are presented for collision energies between 10(-6) and 15,000 cm(-1) using the H2-CO interaction potentials of Jankowski and Szalewicz [J. Chem. Phys. 123, 104301 (2005); 108, 3554 (1998)]. State-to-state cross sections and rate coefficients are reported for the quenching of CO initially in rotational levels j2 = 1-3 by collisions with both para- and ortho-H2. Comparison with the available theoretical and experimental results shows good agreement, but some discrepancies with previous calculations using the earlier potential remain. Interestingly, elastic and inelastic cross sections for the quenching of CO (j2 = 1) by para-H2 reveal significant differences at low collision energies. The differences in the well depths of the van der Waals interactions of the two potential surfaces lead to different resonance structures in the cross sections. In particular, the presence of a near-zero-energy resonance for the earlier potential which has a deeper van der Waals well yields elastic and inelastic cross sections that are about a factor of 5 larger than that for the newer potential at collision energies lower than 10(-3) cm(-1).