Rotationally inelastic scattering of O3-Ar: state-to-state rates with the multiconfigurational time dependent Hartree method

The Chapman cycle, proposed in 1930, describes the various steps in the ongoing formation and destruction of stratospheric ozone. A key step in the formation process is the stabilization of metastable ozone molecules through collisions with a third body, usually an inert collider such as N-2. The "ozone isotopic anomaly" refers to the observation of larger-than-expected atmospheric concentrations for certain ozone isotopologues. Previous studies point to the formation steps as the origin of this effect. A possibly key aspect of the ozone formation dynamics is that of the relative efficiencies of the collisional cooling of different isotopologues. Although the substitution of low-abundance O-18 for O-16 in O-3 molecules corresponds to a relatively small net change in mass, related to this are some subtleties due to symmetry-breaking and a resulting more than doubling of the density of allowed states governed by nuclear-spin statistics for bosons. Recently, a highly accurate 3D potential energy surface (PES) describing O-3-Ar interactions has been constructed and used to benchmark the low-lying rovibrational states of the complex. Here, using this new PES, we have studied the collisional energy-transfer dynamics using the MultiConfiguration Time Dependent Hartree method. A study of the rotationally inelastic scattering was performed for the parent (OOO)-O-16-O-16-O-16-Ar system and compared with that of the (OOO)-O-16-O-16-O-18-Ar isotopologue. The state-to-state cross-sections and rates from the 0(0,0) initial state to low lying excited states are reported. Analysis of these results yields insight into the interplay between small changes in the rotational constants of O-3 and the reduced mass of the O-3-Ar collision system, combined with that of the symmetry-breaking and introduction of a new denser manifold of allowed states.