Photochemical kinetics of excited states of ozone and oxygen: Laboratory studies and atmospheric implications.

Abstract

The photochemistry of O$\sb3$ has matured through the extensive research efforts of the last two decades, but its completeness has been questioned by several laboratory and atmospheric observations, including the unusually complex kinetics for the ozone three-body recombination reaction at high pressures, the unexplained heavy ozone isotope enhancement in the stratosphere, and the deficiencies of current chemical models at 90-120 km. The model deficiencies may be related to several of the excited states of O$\sb3$ and O$\sb2$. In this dissertation, the photochemical kinetics of these excited species have been studied in a series of laboratory measurements, which are divided into two groups: (1) the study of the excited intermediates formed in the ozone recombination reaction, and (2) the investigation of the unusual odd oxygen formation in O$\sb2$ under laser irradiation at 248 nm. The ozone recombination reaction has been investigated at room temperature by monitoring the time-resolved infrared chemiluminescence of ozone at 9.6 $\mu$m, 4.7 $\mu$m, and 3.4 $\mu$m. These studies have indicated that the recombination reaction (O+O$\sb2$+M) apparently proceeds through an intermediate complex OM, and, for M=O$\sb2$, the recombination also involves the participation of a metastable electronic state, O$\sb3$(E). The three infrared emissions have also been used to analyze the deactivation of vibrationally excited O$\sb3$(v). The unusual odd oxygen formation in O$\sb2$ at 248 nm has been studied in both pure O$\sb2$ and O$\sb2$+N$\sb2$ and O$\sb2$+Ar mixtures at pressures between 200 and 1600 torr and at temperatures between 298 and 370$\sp\circ$K. The results have indicated that this odd oxygen formation is initiated by O$\sb2$ absorption in the Herzberg continuum, and it is autocatalytically accelerated by the photodissociation of vibrationally excited O$\sb2$(v) at 248 nm. These kinetics results have been used to study the possible roles of excited O$\sb3$ and O$\sb2$ species in the sources and sinks of odd oxygen at 90-120 km, and in the heavy ozone isotope enhancement in the stratosphere.