Rotationally inelastic scattering of glyoxal by H2 at E=80 meV

Abstract

Using the Monte Carlo classical trajectory (CT) method and the azimuthal close‐coupled, infinite‐order sudden (ACC‐IOS) method, we have calculated cross sections for rotational excitation of S1 trans‐glyoxal by H2 at E=80 meV. The cross sections σ(k=0, j→k’) calculated with the CT method are nearly independent of j. The classical values of σ(k=0, j=5→k’) are in good agreement with the quantum values of σ(k=0→k’) for 2≤k’≤12, although the quantum calculations show a slight preference for odd Δk transitions which is not found in the CT calculations. Both the CT results and the ACC‐IOS results are in good agreement with results obtained in a recent crossed beam experiment. Rotational excitation to high k’ (k’=11,12) occurs by collisions of H2 with one of the H atoms of glyoxal, and the initial value of the orbital angular momentum approximately equals the final value of k in such collisions. Since backward scattering is dominant in collisions leading to high k’, angular momentum constraints alone cannot explain the maximum observed in Δk experimentally (Δk=14).