Low-Energy Molecular Collision Processes in Space

Among the low-energy nonreactive molecular collisions, the rotational and vibrational transitions are the most important inelastic processes. the collision partner is an electron, an ion, or a neutral particle. Depending on the process and the collision system concerned, the magnitude and the energy dependence of the relevant cross sections are widely different. the present status of our knowledge is briefly summarized and some sample cross section data for H2 and CO are shown. Useful relations among the rotational cross sections are indicated. the importance of the long-range intermolecular forces in determining some chemical reaction rates is also pointed out.