Vibrational-state-specific self-relaxation rate constant. Measurements of highly vibrationally excited O2(ν = 19–28)

Abstract

The technique of stimulated emission pumping (SEP) has made the state-specific study of highly vibrationally excited molecules increasingly appealing. A sophisticated spectroscopic probe SEP may also be used as a preparative technique for species with “chemically significant” amounts of vibrational energy. The sensitivity of the approach allows even relatively improbable processes, such as vibrational energy transfer and chemical reaction, to be studied. Recently, highly vibrationally excited oxygen O2(ν) has received attention as a possible source of stratospheric O3 via an autocatalytic mechanism first proposed by Slanger. To evaluate this mechanism, a complete set of vibrational-state-specific vibrational relaxation rate constants are needed for highly vibrationally excited O2(ν) colliding with atmospheric gasses. This information is required in order to determine if solar photodissociation of O2(ν) can compete with collision-induced vibrational re-equilibration. This article will describe recent SEP studies of the vibrational quantum number dependence of the vibrational relaxation of highly vibrationally excited O2 with O2 in the ground vibrational state at 295 and 460 K. These data permit a comparison with recent theoretical models of vibrational relaxation rates and provide indirect evidence for the influence of the vibrationally enhanced endothermic reaction O2(ν>26) + O2(ν = 0) → O3 + O(3P) on the vibrational relaxation rates. The possible implications of these measurements on the autocatalytic stratospheric ozone production model are discussed.