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

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). [ABSTRACT FROM AUTHOR]