Scattering resonances in the rotational excitation of HDO by Ne and normal -H 2 : theory and experiment.

The rotational excitation of a singly deuterated water molecule (HDO) by a heavy atom (Ne) and a light diatomic molecule (H 2 ) is investigated theoretically and experimentally in the near-threshold regime. Crossed-molecular-beam measurements with a variable crossing angle are compared to close-coupling calculations based on high-accuracy potential energy surfaces. The two lowest rotational transitions, 0 00 → 1 01 and 0 00 → 1 11 , are probed in detail and a good agreement between theory and experiment is observed for both transitions in the case of HDO + Ne, where scattering resonances are however blurred out experimentally. In the case of HDO + H 2 , the predicted theoretical overlapping resonances are faithfully reproduced by experiment for the 0 00 → 1 11 transition, while the calculated strong signal for the 0 00 → 1 01 transition is not detected. Future work is needed to reconcile this discrepancy.