Theoretical and experimental investigation of pressure broadening and line shift of carbon monoxide in collision with hydrogen between 8 and 600 K

Abstract

We have measured pressure broadening and line shift parameters for the J=1←0 and J=2←1 transitions of carbon monoxide (CO) in collision with hydrogen (H2) at various temperatures between 8 and 600 K. Because of the abundance of both species in the interstellar medium, the CO–H2 collision system is of astrophysical importance. Measurements below 35 K were made using the collisional cooling technique, while measurements at higher temperatures were made in a conventional equilibrium cell. These measurements were compared with theoretical results of quantum scattering calculations using the currently best available potential surface for the CO–H2 collision system. We find a good agreement between theory and experiment at higher temperatures (>30 K) while for lower temperatures considerable deviations occur.