Rigid-Bender Close-Coupling Treatment of the Inelastic Collisions of H₂O with para-H₂

Abstract

We present a new method taking explicitly into account the coupling between rotation and bending of a nonlinear triatomic molecule colliding with an atom. This approach based on a rigid-bender treatment of the triatomic molecule was originally developed for the case of triatomic molecule linear at equilibrium. It is here extended to the case of a colliding bent triatomic molecule at equilibrium and applied to the case of the para-H2 + H2O inelastic collision using a new H2O-para-H2 adiabatically reduced 4D potential. The results of the method for purely rotational transitions are compared to those of rigid-rotor calculations while vibrational quenching rates of the first exited bending level are calculated for the first time at the close-coupling level.

Rotational relaxation of H2S by collision with He

“…This range of energies could involve exited bending and stretching levels of H 2 S, while the H 2 S vibration is not taken into account in the present work. We know however from previous work (Stoecklin et al 2019) that the state-to-state rotational excitation uncertainty resulting from the use of this approximation above the excited vibrational level thresholds of H 2 S is very small as rovibrational cross sections are two orders of magnitude smaller than purely rotational cross section. Partial waves up to total angular momentum J = 90 were included in the calculations to achieve a 10 −3 relative criterion for the convergence of the state-selected quenching cross section as a function of the maximal value of the total angular momentum quantum number J.…”

“…The dynamics of the system was studied by separately solving the close coupling equation for the two nuclear spin modifications of H 2 S in the space-fixed frame. The calculations were performed with the most recent version of the Newmat code Stoecklin et al (2019) and the log-derivative propagator.…”

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

“…In Nijmegen, measurements are ongoing for the ν 2 ('umbrella') mode of NH 3 [185], and calculations for the rovibrational transitions of CO 2 [186] and C 2 H 2 (Selim et al, in prep). Recently, rovibrational calculations have also been made for H 2 O-H 2 [187] and HCN-He [161], while for species like SO 2 and OH that are commonly observed at mid-IR wavelengths, no data for their mid-IR transitions exist yet. Particularly important are symmetric molecules without a dipole moment such as CH 4 (currently studied by Sahnoun and co-workers) that cannot be observed at (sub)mm wavelengths, but are key players in the organic chemistry of inner disks [188].…”

Cross Sections and Rate Coefficients for Vibrational Excitation of H2O by Electron Impact

“…In all previous works for electron collisions with water, however, vibrational cross-sections were computed for one-quantum transitions only and without considering specific initial and final rotational states. It should be noted, in this context, that Stoecklin and co-workers have recently performed rovibrational state-to-state close-coupling calculations for the quenching of the bending mode (010) of water by (spherical) H 2 [12] and helium atoms [13].…”