Vacuum Ultraviolet Laser-Induced Fluorescence Detection of O(1S) Atom Produced in the 193 nm Photolysis of Ozone

Abstract

The O(2p1S) atoms produced in the photolysis of O3 have been detected by a technique of laser-induced fluorescence spectroscopy with the tunable vacuum ultraviolet (VUV) laser radiation around 121.76 nm. The quantum yield value for O(1S) formation is determined to be (2.5 ± 1.1) × 10-3 in the 193 nm photolysis of O3, which is determined by comparing the VUV laser-induced fluorescence intensities of the O(3s1P1 − 2p1S0) transition with those of the H(2p2Pj ← 1s2S) transition at 121.56 nm of the H atoms generated from the photolysis of HCl at 193 nm. The O(1S) detection technique used in this study is very sensitive, and the detection limit is estimated to be 1 × 109 atoms cm-3. The contribution for the OH radical production from the reaction of H2O with O(1S) produced in the UV photolysis of O3 relative to that from the O(1D) + H2O reaction has been estimated as a function of altitude in the stratosphere, using the photolytic O(1S) quantum yield value obtained in this study and the O(1S) reaction rate coefficients reported previously. The maximum contribution of the O(1S) reaction to OH production rate is a 14% fraction of that from the O(1D) reaction at 40 km altitude at mid-latitudes, assuming the spin-forbidden dissociation process, O(1S) + O2(X3Σg-), for the formation of O(1S) in the photolysis of ozone. Importance of precise measurements of the temperature-dependent reaction rates for O(1S) has been suggested.