Potential energy surface and rotational cross sections for methyl formate colliding with helium.

A potential energy surface for helium interacting with methyl formate has been computed using high-level electronic structure methods. The interaction energies obtained on a three-dimensional grid have been fitted by an analytic function of interatomic distances with correct asymptotic behavior for large intermonomer separations. This potential has then been refitted using partial wave expansion in terms of the distance between centers of mass and spherical angles. The latter potential has been used to compute cross sections for the rotational excitations of methyl formate at the full quantum close-coupling level. Collisional propensity rules and astrophysical implications are discussed.