Quantum study of the bending relaxation of H2O by collision with H

Abstract

Vibrationally excited levels of the H2O molecule are currently detected in various environments of the interstellar medium (ISM), and collisional data for H2O, including vibration with the main colliders of the ISM, are needed. The present study focuses on the bending relaxation of H2O by collision with H when taking bending–rotation coupling explicitly into account with the rigid-bender close-coupling (RB-CC) method. With this aim, a new four-dimensional potential energy surface including the H2O bending mode is developed from a large grid of ab initio energies computed using a high level of theory. For purely rotational transitions, our RB-CC rates show very good agreement with rigid-rotor calculations performed using our new potential energy surface (PES) and with those available in the literature. Calculations for pure rotational transitions inside the excited bending level ν2 = 1 of H2O are performed and compared with their equivalents inside ν2 = 0. Vibrational quenching of H2O is also calculated and found to be much more efficient through collision with H rather than with He.

A Rigid Bender Study of the Bending Relaxation of H2O and D2O by Collisions with Ar

“…They used a full dimensional PES [16] and studied the vibrational relaxation of the system using the CC method and tested the validity of the Rigid Rotor Approximation for n 2 ¼ 0; n 2 ¼ 1 levels. While this latter study demonstrated that full dimensional calculations are possible for this system, the coupling between bending and stretching is quite small in the n 2 ¼ 1 state making possible to carry out scattering calculations using the Rigid-Bender approximation [17] in order to compare our results with the experimental works available as was already done successfully for the collisions of H 2 O with He [18] and H. [19] The other important objective of the present work is to study the inelastic collision of Ar with D 2 O and to compare the two systems as the only study investigating these effects was done using a semi-classical approach. [12] To this aim two 4D PES for Ar-H 2 O and Ar-D 2 O, including an explicit dependence on the bending angle are developed.…”

“…The Close Coupling calculations were carried out separately for each of the ortho‐ and para‐ forms of H 2 O/D 2 O using our new PES and the Newmat code, [17] following the same methodology than in our previous works [17–19] . We performed both rigid rotor (RAST‐CC) and rigid bender (RB‐CC) calculations.…”

“…The Close Coupling calculations were carried out separately for each of the ortho-and para-forms of H 2 O/D 2 O using our new PES and the Newmat code, [17] following the same methodology than in our previous works. [17][18][19] We performed both rigid rotor (RAST-CC) and rigid bender (RB-CC) calculations. The basis set describing the H 2 O/D 2 O molecules included 10 values of the rotational quantum number j for the RAST-CC calculations while the RB-CC one included 10 values of the rotational quantum number j inside each of the two first vibrational bending levels.…”

An explicitly correlated six-dimensional potential energy surface for the SiCSi + H2 complex

“…Additionally, the low vibrational frequency of SiCSi (o = 202 cm À1 ) 13 suggests that the inclusion of a bending motion in the close coupling calculations can affect the rate coefficients, as in the case of C 3 + He. 19 The rigid bender close-coupling method [20][21][22] requires a PES with an explicit dependence of the bending angle. If both molecules, SiCSi and H 2 , are considered rigid rotors, the expansion of the surface in the appropriate angular basis is far from being a straightforward procedure.…”

“…Fitting coefficients of eqn(22) for the classical and semiclassical second virial coefficients (in cm 3 mol À1 ) This journal is © the Owner Societies 2023Finally, the computed B 12 coefficients were fitted to…”