Bending Relaxation of H₂O by Collision with Para‐ and Ortho‐H₂

Abstract

We extend our recent theoretical work on the bending relaxation of H2O in collisions with H2 by including the three water modes of vibration coupled with rotation, as well as the rotation of H2. Our full quantum close‐coupling method (excluding the H2 vibration) is combined with a high‐accuracy nine‐dimensional potential energy surface. The collisions of para‐H2O and ortho‐H2O with the two spin modifications of H2 are considered and compared for several initial states of H2O. The convergence of the results as a function of the size of the rotational basis set of the two colliders is discussed. In particular, near‐resonant energy transfer between H2O and H2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with = , and being respectively the H2 initial and final rotational quantum numbers. Finally, the calculated value of the H2O bending relaxation rate coefficient at 295 K is found to be in excellent agreement with its experimental estimate.

First close-coupling study of the excitation of a large cyclic molecule: collision of c-C5H6 with He

“…rigid-rotor approximation). As it was shown earlier on the example of H 2 O 21 and HCN, 22 the explicit consideration of the vibrational modes in the PES has no significant impact on the pure rotational transitions, even at collision energies above the first vibrational excitation threshold (note that the lowest anharmonic vibrational frequency of c-C 5 H 6 is about 520 cm −1 23 ). To define the collisional complex, a 3D Jacobi coordinate system ( R , θ , ϕ ) has been chosen (see Fig.…”