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

We extend our recent theoretical work on the bending relaxation of H2O in collisions with H-2 by including the three water modes of vibration coupled with rotation, as well as the rotation of H-2. Our full quantum close-coupling method (excluding the H-2 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 H-2 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 H-2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with Delta j(2 )+ j(2)(f) - j(2)(i) = +2, +4, j(2)(i) and j(2)(i)f being respectively the H-2 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.