Dissociation dynamics of the HCl dimer ion

The dissociation pathways of (HCl)2+ are studied by a molecular beam-femtosecond multiphoton ionization technique, and via ab initio calculations at the MP2/6-31G(d,p) level and using Gaussian-2 theory. Results indicate, besides the commonly accepted proton-transferred HClH+Cl structure, a hydrogen-peroxide-like structure, (HCl–ClH)+, also exists and appears to be more stable. Their interconversion involves a barrier of 0.24 eV. A new dissociation product, Cl2+, is observed and shown to come from an intracluster reaction of the HCl dimer cation. Dissociations of the (HCl)2+ into H2Cl+ and HCl+ channels are preferred at low internal excitations, whereas dissociations into Cl2+ and HCl2+ require higher excitation energies.