Internal energy dependence of the photodissociation dynamics of O-3(-) using cryogenic photoelectron-photofragment coincidence spectroscopy

摘要

Photoelectron-photofragment coincidence (PPC) spectra of ozonide, O-3(-) , were measured at 388 nm (E-hv = 3.20 eV) using a newly constructed cryogenic octopole accumulation trap coupled to a PPC spectrometer. The photoelectron spectra reveal three processes consisting of a stable photodetachment channel, and two distinct photodissociation pathways yielding (1) O-2 + O- or (2) O + O-2(-). The first photodissociation pathway is observed in the PPC spectra by photodetachment of the O fi product by a second photon, and produces electronically excited O-2((1)Delta(g)). The O-2(-) fi product of the second photodissociation pathway undergoes autodetachment for O-2(-) ((2)Pi(g), v '' > 4), a process greatly enhanced by vibrational excitation of the precursor O-3(-). Cooling anions thermalized at 300 K to < 17 K in a cryogenic octopole accumulation trap essentially turns off this autodetachment pathway. The product kinetic energy distribution in coincidence with the autodetached electrons from O-2(-) (v '' = 4) exhibits resolved features consistent with bend (v(2)), asymmetric stretch (v(3)) and a stretching combination band (v(1) + v(3)) in the intermediate electronic state, illustrating the insights that can be gained from kinematically complete measurements. These results are discussed in the context of the low-lying excited states of O-3(-). Published by AIP Publishing.