The rotationalexcitation by helium of methanol in its ground and first excitedtorsional states

Abstract

We have improved and extended our previous calculations of cross sections for the rotational excitation of methanol by helium. Inthe case of methanol in its torsional ground state, we extendedour coupled states computations of the cross sections to highercollision energies and larger rotational basis sets. Theaccuracy of the rotational energy levels and eigenfunctions hasbeen reviewed and improved for A-type methanol. The calculationshave been extended to A- and E-type methanol in their firstexcited torsional states by averaging the CH3OH-Heinteraction potential over the excited state torsionaleigenfunctions. Thermal rate coefficients have been calculatedat low temperatures. Predictions are made of line intensityratios which are sensitive to the density of the He perturberand which lend themselves to the determination of the perturberdensities in the dark molecular clouds of the interstellarmedium.