Dissociative recombination of H3O+

Ab initio molecular orbital calculations have been performed on potential e nergy surfaces associated with products of dissociative recombination (DR) of H3O+ + e(-) experiments carried out in the ASTRID heavy-ion storage ring . Gradient geometry optimizations and frequency calculations on critical po ints on the H3O ground-electronic-state surface and its dissociation paths were performed at levels of theory up to and including MP2(full)/6-311G(d,p ) with extra diffuse functions added to the oxygen atom; single-point calcu lations subsequently were performed at levels up to CCSD(T) with the same b asis set. Dissociation pathways of the two lowest-energy valence-to-Rydberg H3O excited states were studied using CIS single-point calculations on SCF -level optimized geometries along ground-state H3O dissociation pathways, a nd no barriers to fragmentation were observed. The most exothermic ground-s tate dissociation pathway connects H3O to H2O (X(1)A(1)) + H; however, OH(X (2)Pi) + H-2 and OH(X(2)Pi) + 2H also are energetically accessible products . Dissociation of the two valence-to-Rydberg electronically excited H3O spe cies lead to these same products but also lead to products (OH(A(2)Sigma) H-2, OH(A(2)Sigma) + 2H) which are energetically inaccessible from grounds tate H3O. These computational results provide a detailed understanding of t he intricacies of the observed experimental processes, and suggest future e xperimental investigations on the subject.