Vibrational Relaxation of D2O Induced by Collision with He: A Rigid Bender Close Coupling Study.

The vibrational relaxation of the first excited bending state of D2O induced by collision with He is studied at the close coupling level and using the Rigid Bender approximation. A new 4D potential energy surface is calculated and reported for this system. It is then used to determine the low-lying bound states of the D2O-He van der Waals complex and to perform scattering calculations. Collision rates are determined for pure rotational transitions as well as for rovibrational transitions within the first excited bending state. The results are compared with those obtained for the collision of D2O with other noble gases such as Ne and Ar. We also analyse the differences observed with respect to the H2O+He collisions and compare our results with experiment.

Scattering resonances in the rotational excitation of HDO by Ne and normal-H2: theory and experiment.

The rotational excitation of a singly deuterated water molecule (HDO) by a heavy atom (Ne) and a light diatomic molecule (H2) is investigated theoretically and experimentally in the near-threshold regime. Crossed-molecular-beam measurements with a variable crossing angle are compared to close-coupling calculations based on high-accuracy potential energy surfaces. The two lowest rotational transitions, 000 → 101 and 000 → 111, are probed in detail and a good agreement between theory and experiment is observed for both transitions in the case of HDO + Ne, where scattering resonances are however blurred out experimentally. In the case of HDO + H2, the predicted theoretical overlapping resonances are faithfully reproduced by experiment for the 000 → 111 transition, while the calculated strong signal for the 000 → 101 transition is not detected. Future work is needed to reconcile this discrepancy.

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

The bending relaxation of H2O and D2O by collisions with Ar is studied at the Close Coupling level. Two new 4D PES are developed for these two systems. They are tested by performing rigid rotor calculations as well as by computing the D2O-Ar bound states. The results are compared with available theoretical and experimental data. Propensity rules for the dynamics are discussed and compared to those of H2O colliding with Ne or He. The bending relaxation cross sections and rates are then calculated for these two systems. The results are analysed and compared with available experimental data.

Bending Relaxation of H2 O by Collision with Para- and Ortho-H2.

We extend our recent theoretical work on the bending relaxation of H2 O 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-H2 O and ortho-H2 O with the two spin modifications of H2 are considered and compared for several initial states of H2 O. 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 H2 O and H2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with Δ j 2 = j 2 f - j 2 i ${{\rm{\Delta }}j_2 = j_2^f - j_2^i }$ = + 2 , + 4 ${ + 2, + 4}$ , j 2 i ${j_2^i }$ and j 2 f ${j_2^f }$ being respectively the H2 initial and final rotational quantum numbers. Finally, the calculated value of the H2 O bending relaxation rate coefficient at 295 K is found to be in excellent agreement with its experimental estimate.

A Comparative Study of the Cold Collisions of H2O and D2O with Ne.

The present work is dedicated to the first theoretical study of the rotationally inelastic collisions of Ne with H2O and its isotopologue D2O in an attempt to analyze the effect on the dynamics of H substitution by deuterium. To this aim two new potential energy surfaces are developed. Their quality is tested by computing the bound states of the complexes and comparing them with those most recently reported by other teams. System-specific collisional propensity rules are inferred for these two systems by analyzing the computed state-to-state cross sections at low and higher collision energy. The application of the Alexander parity index propensity rule is also discussed, and the present results are compared with those obtained for the collisions with other noble gases.