State-to-state rovibrational transition rates for CO2 in the bend mode in collisions with He atoms.

Modeling environments that are not in local thermal equilibrium, such as protoplanetary disks or planetary atmospheres, with molecular spectroscopic data from space telescopes requires knowledge of the rate coefficients of rovibrationally inelastic molecular collisions. Here, we present such rate coefficients in a temperature range from 10 to 500 K for collisions of CO2 with He atoms in which CO2 is (de)excited in the bend mode. They are obtained from numerically exact coupled-channel (CC) calculations as well as from calculations with the less demanding coupled-states approximation (CSA) and the vibrational close-coupling rotational infinite-order sudden (VCC-IOS) method.

Efficient computational methods for rovibrational transition rates in molecular collisions.

Astrophysical modeling of processes in environments that are not in local thermal equilibrium requires the knowledge of state-to-state rate coefficients of rovibrational transitions in molecular collisions. These rate coefficients can be obtained from coupled-channel (CC) quantum scattering calculations, which are very demanding, however. Here, we present various approximate but more efficient methods based on the coupled-states approximation (CSA), which neglects the off-diagonal Coriolis coupling in the scattering Hamiltonian in body-fixed coordinates.

Multi-channel distorted-wave Born approximation for rovibrational transition rates in molecular collisions.

Modeling protoplanetary disks and other interstellar media that are not in local thermal equilibrium require the knowledge of rovibrational transition rate coefficients of molecules in collision with helium and hydrogen. We present a computational method based on the numerically exact coupled-channel (CC) method for rotational transitions and a multi-channel distorted-wave Born approximation (MC-DWBA) for vibrational transitions to calculate state-to-state rate coefficients. We apply this method to the astrophysically important case of CO-He collisions, using newly computed ab initio three-dimensional potential energy surfaces for CO-He with CO distorted along the symmetric and asymmetric stretch (ν and ν) coordinates.