Reactive Scattering Resonances in (He,H ⁺₂ ) Collisions

Abstract

Resonances in atomic and molecular collisions have been receiving a lot of attention in the last few decades.1 Reactive scattering resonances in collinear (He,H ⁺₂ ) collisions were pointed out first by Kouri and Baer2 and they have been the subject of a large number of theoretical and experimental investigations since.3 The reason for such an interest is the ubiquitous nature of ion-molecule reactions in ionosphere and in interstellar media and the (He,H ⁺₂ ) system serves as a prototype. A reasonably accurate (±1 kcal/mol) ab initio potential-energy surface (PES) for the system was published by McLaughlin and Thompson4 and an analytic representation of comparable accuracy to it was reported by Joseph and Sathyamurthy.5 The resulting McLaughlin-Thompson-Joseph-Sathyamurthy (MTJS) PES has been used in a large number of quasiclassical trajectory and quantum mechanical investigations.3 An improved analytic fit to the same set of ab initio potential energy values was published by Aguado and Paniagua6 a few years ago. More recently, Palmieri et al7 have published, perhaps, the most accurate ab initio PES for the system. In this paper, we review the progress made in characterising and understanding the nature of reactive scattering resonances in collinear as well as three dimensional (He,H ⁺₂ ) collisions and report some of the recent results from our laboratory.