Charged Particle Imaging of the Deprotonated Octatrienoic Acid Anion: Evidence for a Photoinduced Cyclization Reaction

Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9-CO2](-), shows the formation of [C7H9](-) and loss of H- at hv = 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 hv = 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 Hat hv = 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.