Journal of Physical Chemistry A, Vol.120, No.40, 7828-7838, 2016
Photoelectron Imaging Spectra of O-2(-)center dot VOC and O-4(-)center dot VOC Complexes
The anion photoelectron imaging spectra of O-2(-). VOC and O-4(-)center dot VOC (VOC = hexane, isoprene, benzene, and benzene-d(6)) complexes measured using 3.49 eV photon energy, along with the results of ab initio and density functional theory results are reported and analyzed. Photodetachment of these anionic complexes accesses neutrals that model collision complexes, offering a probe of the effects of symmetry-breaking collision events on the electronic structure of normally transparent neutral molecules. The energies of O-4(-)center dot VOC spectral features compared to the bare O-2(-) indicate that photodetachment of the anion accesses a modestly repulsive region of the O-2-VOC potential energy surface, with subtle VOC dependence on the relative energies of the O-2 (X-3 Sigma(-)(g))center dot VOC ground state and O-2 (a (1)Delta(g))center dot VOC excited state. In contrast, a significantly higher intensity of the transition to the O-2 (a (1)Delta(g))center dot VOC excited state relative to the O-2 (X-3 Sigma(-)(g))center dot VOC ground state is observed for VOC = benzene, with a less pronounced effect observed for VOC = isoprene. Similar spectral effects are observed in the O-4(-). benzeneand O-4(-) isoprene PE spectra. Several explanations are considered, with involvement of a temporary anion state emerging as the most plausible.