Quantum mechanical and astrophysical studies of methanol

¹ Physics Department, The University, Durham, DH1 3LE, UK
² IAS (UMR 8617), Université de Paris–Sud, F-91405 Orsay, France

^a e-mail: david.flower@durham.ac.uk

Abstract

Interstellar methanol has been observed extensively at radio frequencies from the ground, and, very recently, it has been observed at higher frequencies, by means of the Herschel satellite. Being a complex molecule, methanol has a rich spectrum exhibiting rotational and internal torsional motions. However, by the same token, the determination of the cross sections and rate coefficients for the excitation of methanol by the principal perturbers, helium and molecular hydrogen, is a far from trivial task. We have recently extended and considerably improved previous calculations of these data. In the case of molecular hydrogen, results are now available for the excitation of both A- and E-type methanol, not only by para- but also by ortho-H₂. These data have been used to model the HIFI observations of the outflow source L1157 B1. The methanol emission is computed self-consistently, in parallel with the dynamics and the chemistry, allowing for the optical depths in the emission lines by means of the LVG approximation. The results of these calculations are summarized.