Low energy H+CO scattering revisited: CO rotational excitation with new potential surfaces

Abstract

A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0->1 rotational transition. New close-coupling (CC) rigid-rotor calculations for CO(v=0,J=0) excitation by H are performed on four different PESs. Two of the PESs are obtained in this work using state-of-the-art quantum chemistry techniques at the CCSD(T) and MRCI levels of theory. Cross sections for the J=0->1, as well as other odd Delta J, transitions are significantly suppressed compared to even Delta J transitions in thermal energy CC calculations using the CCSD(T) and MRCI surfaces. This is consistent with a expected even Delta J propensity and in contrast to CC calculations using the earlier WKS PES which predict a dominating 0->1 transition. The current results suggest that the original astrophysical assumption that excitation of CO by H_2 dominates the kinetics of CO in diffuse ISM gas is likely to remain valid.

arXiv comment3 figures

Cited by in corpus (15)

• Rotational quenching of CO due to H${}_2$ collisions
• Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
• First detection of CO in a high-redshift DLA
• Formation, fractionation and excitation of carbon monoxide in diffuse clouds
• Diffuse Molecular Cloud Densities from UV Measurements of CO Absorption
• Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope
• On the Validity of Collider-Mass Scaling for Molecular Rotational Excitation
• Quantum Calculation of Inelastic CO Collisions with H: I. rotational quenching of low-lying rotational levels
• The detectability of mm-wave molecular rotational transitions
• Quantum Calculation of Inelastic CO Collisions with H. III. Rate Coefficients for Ro-vibrational Transitions
• Collisional excitation of water by hydrogen atoms
• Formation and Fractionation of CO (carbon monoxide) in diffuse clouds observed at optical and radio wavelengths
• The Ratio of CO to Total Gas Mass in High Redshift Galaxies
• Rotational Excitation of polar molecules by H2 and electrons in diffuse clouds
• Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150