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A recent modeling study of brightness ratios for CO rotational transitions ingas typical of the diffuse ISM by Liszt found the role of H collisions to bemore important than previously assumed. This conclusion was based on quantumscattering calculations using the so-called WKS potential energy surface (PES)which reported a large cross section for the important 0->1 rotationaltransition. 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 areobtained in this work using state-of-the-art quantum chemistry techniques atthe CCSD(T) and MRCI levels of theory. Cross sections for the J=0->1, as wellas other odd Delta J, transitions are significantly suppressed compared to evenDelta J transitions in thermal energy CC calculations using the CCSD(T) andMRCI surfaces. This is consistent with a expected even Delta J propensity andin contrast to CC calculations using the earlier WKS PES which predict adominating 0->1 transition. The current results suggest that the originalastrophysical assumption that excitation of CO by H_2 dominates the kinetics ofCO in diffuse ISM gas is likely to remain valid.

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