Rotational excitation of HDO and D2O by H2: Experimental and theoretical differential cross-sections
Abstract
We present state-to-state differential cross sections (DCSs) for rotationally inelastic scattering of HDO by normal- and para-H2 at collision energies of 580 cm-1 and 440 cm-1. (2+1) resonance enhanced multiphoton ionization is used to detect rotationally cold HDO molecules before collision and as scattering products, which occupy higher rotational states due to collision with H2. Relative integral cross sections of HDO are obtained by integrating its DCSs measured at the same experimental conditions. Experimental and theoretical DCSs of HDO scattered by normal- and para-H2 are in good agreement in 30°-180° range of scattering angles. This partial agreement shows the accuracy of the recently tested potential of H2O-H2, but now by using a completely different set of rotational transitions that are (unlike in H2O), not forbidden by nuclear spin restrictions. Similar results are presented for D2O scattered by normal-H2 at collision energy of 584 cm-1. The agreement between experiment and theory is, however, less good for forward scattering of HDO/D2O. A critical analysis of this discrepancy is presented.