Photodissociation dynamics of fulvenallene and the fulvenallenyl radical at 248 and 193 nm

Abstract

Photofragment translational spectroscopy was used to study the photodissociation of fulvenallene, C₇H₆, and the fulvenallenyl radical, C₇H₅, at 248 nm and 193 nm. Starting from fulvenallene, only the H-atom loss channel producing the fulvenallenyl radical, C₇H₅, was observed. Fulvenallene dissociation occurs on the ground state surface with no exit barrier, and there is good agreement between our experimentally determined photofragment translational energy distribution and a prior distribution for a statistical process. Subsequent absorption at both wavelengths by fulvenallenyl enabled investigation of the photodissociation of this radical. Two channels were observed: C₅H₃ + C₂H₂ and C₄H₂ + C₃H₃. The photofragment translational energy distributions for these channels are peaked away from 0 kcal mol⁻¹, which is consistent with ground state dissociation over an exit barrier. At 248 nm, the C₃H₃-loss channel accounted for 85 ± 10% of fulvenallenyl dissociation, while at 193 nm it accounted for 80 ± 15%. The experimental branching between these channels is in reasonable agreement with Rice–Ramsperger–Kassel–Marcus theory calculations, which predict C₃H₃-loss to account for 70% and 63% of dissociation for 248 nm and 193 nm respectively.