Dissociation of the phenylarsane molecular ion: A theoretical study

The potential energy surfaces (PESs) for the primary and secondary dissociations of the phenylarsane molecular ion (1a) were determined from the quantum chemical calculations using the G3(MP2)//B3LYP method. Several pathways for the loss of H• were determined and occurred though rearrangements as well as through direct bond cleavages. The kinetic analysis based on the PES for the primary dissociation showed that the loss of H₂ was more favored than the loss of H•, but the H• loss competed with the H₂ loss at high energies. The bicyclic isomer, 7-arsa-norcaradiene radical cation, was formed through the 1,2 shift of an α-H of 1a and played an important role as an intermediate for the further rearrangements in the loss of H• and the losses of As• and AsH. The reaction pathways for the formation of the major products in the secondary dissociations of [M-H]⁺ and [M-H₂]^+• were examined. The theoretical prediction explained the previous experimental results for the dissociation at high energies but not the dissociation at low energies.