Collisional excitation of interstellar molecules

Abstract

An effective straight-line trajectory (EST) approach has been proposed for computation of collision-induced rotational line widths (half widths at half maximum) and excitation rates in case of atom-molecule system under the frame work of Smithet. al. (1976) formalism and molecule-molecule systems under the framework of a normalized semi-classical perturbative approach. An arbitrary multiplication factor RX with its optimum value can be used as a measure of significance of the curved trajectories of the colliding particles. The EST approach has been tested for HCL-Ar system and further applied to CO-He, CO-H2, and OCS-H2 systems of interstellar interest. The line width computations in case of HCl−Ar system are in accordance with the trend of the experimental values. The results obtained by the present approach are in good agreement with the theoretical computations using semi-perturbative approach. The present approach provides significant information about the lower and upper bound of the collision-induced rates even for the perturbers in rotationally excited states. The EST approach is not expensive in nature. It can be generalized for vibrational-electronic excitations.