Photochemistry of O(3)- and dissociation dynamics of the low-lying excited states of O(3).

摘要

This thesis presents a study of the photochemistry of the ozone anion, O{dollar}sb3sp-{dollar}, at 523 and 532 nm and the dissociation dynamics of the low-lying excited states of ozone at 266 nm using photoelectron and photofragment translational energy spectroscopies in a mass-selected fast-ion beam. Photon interactions with negative ions can cause variations in the electron density of the D region of the ionosphere. To attain a greater understanding of the photochemical interaction of O{dollar}sb3sp-{dollar} in the ionosphere, the dissociation dynamics for the process O{dollar}sb3sp-{dollar} h{dollar}nu{dollar}, {dollar}to{dollar} O{dollar}sp-{dollar} + O{dollar}sb2{dollar} are examined. In these experiments evidence for isomeric forms of O{dollar}sb3sp-{dollar} are observed.; The low-lying excited states of neutral ozone also have important atmospheric implications. The possibility of a bound low-lying electronic state has been suggested to explain disagreement in the experimentally determined ozone recombination rates. In the experiments described here, photoelectron spectra are acquired in coincidence with a single particle at the beam velocity to examine the stability of the excited states. Kinetic energy distributions are also examined to place an upper limit of 0.5 {dollar}mu{dollar}s for the lifetime of the low-lying excited states of O{dollar}sb3{dollar}. Dissociative photodetachment of O{dollar}sb3sp-{dollar} (O{dollar}sb3sp-{dollar}(X{dollar}sp2{dollar}B{dollar}sb1{dollar}) {dollar}to{dollar} O({dollar}sp3{dollar}P) + O{dollar}sb2(sp3Sigmasbsp{lcub}rm g{rcub}{lcub}-{rcub}{dollar}) + e{dollar}sp-{dollar}) at 266 nm is used to study the dynamics of the low-lying excited states of ozone. Photoelectron-photofragment correlation spectra show that the {dollar}rm sp3Asb2{dollar} and {dollar}rm sp3Bsb2{dollar} states dissociate with nearly all of the available energy appearing in translation. Evidence for non-adiabatic dissociation of the {dollar}rm sp3Bsb1{dollar} state to ground state O({dollar}sp3{dollar}P) + O{dollar}sb2(sp3Sigmasb{lcub}rm g{rcub}{lcub}sp-{rcub}){dollar} products is also observed.; Additional dissociation dynamics studies for isotopically substituted ozone are presented to examine the possible role of triplet states in mass-independent isotope effects. These experiments did not reveal striking changes in the dissociation dynamics of the excited electronic states for isotopically substituted O{dollar}sb3{dollar}. However, a photofragment branching ratio of 3:4 for {dollar}sp{lcub}18{rcub}{dollar}O + {dollar}sp{lcub}32{rcub}{dollar}O{dollar}sb2{dollar} to {dollar}sp{lcub}16{rcub}{dollar}O + {dollar}rm sp{lcub}34{rcub}Osb2{dollar} is observed. This ratio is compared to a pure statistical ratio and a ratio derived from quantitative enrichments.