Inelastic collisions of interstellar molecules

Abstract

The rotational energy transfer of NH3, OH and D2CO in inelastic collisions with He and H2 is studied in a crossed molecular beam experiment. The molecules are prepared in a single initial state by rotational cooling in an adiabatic expansion followed by electrostatic state selection. Relative state-to-state cross sections are determined by measuring the collision induced redistribution of the population of the initial state by using state selective laser detection techniques. The results for NH3 and OH are compared to theoretical values obtained from quantum calculations. Except for NH3 — He where theory predicts a parity selection rule for transitions to the 33 and 43 states, which is not observed in the experiment, good agreement between experiment and theory is obtained.