Rotational excitation of HDO and D₂O by H₂: Experimental and theoretical differential cross-sections

Gautam Sarma , Chung-Hsin Yang , Ashim Kumar Saha , David H. Parker , Laurent Wiesenfeld (1)

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

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.

Keywords: deuterium compounds; hydrogen compounds; hydrogen neutral molecules; multiphoton processes; photoionisation; rotational states; 33.80.Rv; 33.15.Mt; 33.20.Sn; Multiphoton ionization and excitation to highly excited states; Rotation vibration and vibration-rotation constants; Rotational analysis

Domains: Sciences of the Universe [physics]

Gautam Sarma, Chung-Hsin Yang, Ashim Kumar Saha, David H. Parker, Laurent Wiesenfeld. Rotational excitation of HDO and D₂O by H₂: Experimental and theoretical differential cross-sections. Journal of Chemical Physics, 2013, 138, pp.024314-024314. ⟨10.1063/1.4772600⟩. ⟨insu-03617526⟩