Rotational Excitation of HCN by Collisions

Rate constants for rotational excitation of HCN by collisions with low-energy He atoms (kinetic temperatures below 100 K) have been computed from first principles. The accuracy of individual rates is conservatively estimated to be I 30 percent above 30 K and within a factor of 2 below 20 K. These rates are also believed to be representative of excitation by collisions with H2. Subject headings: interstellar matter - molecules, interstellar - transition probabilities