Context. The study of noble gas compounds has gained renewed interest thanks to the recent detection of ArH+ in the interstellar medium (ISM). The analysis of physical-chemical conditions in the regions of the ISM where ArH+ is observed requires accurate collisional data of ArH+ with He, H2, electrons, and H. Aims. The main goals of this work are to compute the first three-dimensional potential energy surface (PES) to study the interaction of ArH+ with He, analyze the influence of the isotopic effects in the rate coefficients, and evaluate the rovibrational relaxation rates. Methods. Two ab initio grids of energy were computed at the coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) level of theory using the augmented correlation consistent polarized quadruple, and quintuple zeta basis sets (aug-cc-pVQZ, and aug-cc-pV5Z) and a grid at the complete basis set limit was determined. The analytical representation of the PES was performed using the reproducing kernel Hilbert space (RKHS). The dynamics of the system was studied using the close coupling method. Results. The differences in the rate coefficients for the isotopes 36ArH+, 38ArH+, and 40ArH+ in collision with He are negligible. However, the rotational rates for the collision of ArD+ with He cannot be estimated from those for ArH++He. Comparison with previous rates for the 36ArH++He collision showed discrepancies for ∣ Δj ∣ > 2, and in the case of high initial rotational states of 36ArH+ differences were found even for ∣ Δj ∣ = 1. The rates for transitions between different vibrational states were also examined. Finally, new sets of rotational rates for 36ArH++He and 36ArD++He are reported.

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.