Charged particle imaging of the deprotonated octatrienoic acid anion : evidence for a photoinduced cyclization reaction.

Abstract

Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9–CO2]−, shows the formation of [C7H9]− and loss of H– at hν = 4.13 eV. Using velocity map imaging, the H– fragment was characterized to have a Boltzmann-like kinetic energy distribution consistent with dissociation on a ground electronic state. Similar dynamics were not observed at hν = 4.66 eV even though there is clear evidence for recovery of the ground electronic state of [C7H9–CO2]−. In accord with supporting electronic structure calculations, the production of H– at hν = 4.13 eV is explained by excited-state dissociation of CO2 to form [C7H9]−, which subsequently undergoes a ring-closure isomerization reaction to yield toluene and H–. These data represent the first evidence for a photoinduced ring-closing isomerization reaction in an anionic polyene and provides an interesting example of the rich anion dynamics that can occur in the detachment continuum and that can influence photochemistry.