A full nine-dimensional potential-energy surface for hydrogen molecule-water collisions

Abstract

The hydrogen and water molecules are ubiquitous in the Universe. Their mutual collisions drive water masers and other line emission in various astronomical environments, notably molecular clouds and star forming regions. We report here a full nine-dimensional interaction potential for H 2 O−H 2 calibrated using high-accuracy, explicitly correlated wavefunctions. All degrees of freedom are included using a systematic procedure transferable to other small molecules of astrophysical or atmospherical relevance. As a first application, we present rate constants for the vibrational relaxation of the v 2 bending mode of H 2 O obtained from quasi-classical trajectory calculations in the temperature range 500−4000 K. Our high temperature (T ≥ 1500 K) results are found compatible with the single experimental value at 295 K. Our rates are also significantly larger than those currently used in the astrophysical literature and will lead to a thorough re-interpretation of vibrationally excited water emission spectra from space.

Rotational excitation of ortho-H2O by para-H2 (j2 = 0, 2, 4, 6, 8) at high temperature

“…As was pointed out in Faure et al (2005a), this state-averaged PES is actually very close to a rigid-body PES using state-averaged geometries for H 2 O and H 2 .…”

“…The new PES of Faure et al (2005a) leads to a significant re-evaluation of the rate coefficients for the excitation of H 2 O by para-H 2 ( j = 0). Indeed for the 1 10 to 1 01 transition observed by the SWAS satellite, the new PES increases the de-excitation rate coefficient by a factor of 4 at 5 K and by 75% at 20 K compared to the previous results of Dubernet et al (Dubernet & Grosjean 2002;Grosjean et al 2003), leading to a total increase at 20 K of 185% with respect to the Phillips et al (1996) results.…”

“…Recently an accurate 9D PES for the deformable H 2 -H 2 O system was calculated by Faure et al (2005a). This PES combined conventional 5D and 9D CCSD(T) calculations (coupled cluster with perturbative triples) and accurate calibration data using the explicitely correlated CCSD(T)-R12 approach (Noga & Kutzelnigg 1994).…”

“…As a first application of the 9D PES, high temperature (1500 K < T < 4000 K) rate coefficients for the relaxation of the ν 2 bending mode of H 2 O were estimated from quasiclassical trajectory calculations (Faure et al 2005a) and the role of rotation in the vibrational relaxation of water was emphasized (Faure et al 2005b).…”

Overtone vibrational spectroscopy in H2-H2O complexes: A combined high level theoretical ab initio, dynamical and experimental study

“…A potential energy surface (PES) for H 2 -H 2 O that includes all nine internal degrees of freedom has been calculated ab initio by Valiron et al 1,47 with the use of the CCSD(T)-R12 method (coupled-cluster with singles, doubles, and perturbative triples, explicitly correlated). This PES is independent of nuclear mass and can be employed for any of the water-hydrogen isotopologues.…”