Ab initio and RRKM study of photodissociation of azulene cation

Abstract

The ab initio/Rice–Ramsperger–Kassel–Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of the azulene cation at different values of the photon energy. Reaction pathways leading to various decomposition products have been mapped out at the G3(MP2,CC)//B3LYP level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for the dissociation products have been calculated using the steady-state approach. The results show that a photoexcited azulene cation can readily isomerize to a naphthalene cation. The major dissociation channels are elimination of atomic hydrogen, an H₂ molecule, and acetylene. The branching ratio of the H elimination channel decreases with an increase of the photon energy. The branching ratio of the acetylene elimination as well as that of the H₂ elimination rise as the photon energy increases. The main C₈H₆⁺ fragment at all photon energies considered is a pentalene cation, and its yield decreases slightly with increasing excitation energy, whereas the branching ratios of the other C₈H₆⁺ fragments, phenylacetylene and benzocyclobutadiene cations, grow.