Quantum yield for N(4S) production in the ultraviolet photolysis of N2O

Abstract

Direct detection of N(4S) atom formation in the 193 nm photolysis of N2O by a technique of vacuum ultraviolet (vuv) laser‐induced fluorescence spectroscopy has been reported. Tunable vuv laser radiation around 120.071 nm that is resonant to the one‐photon N(2p23s 4P1/2 − 2p3 4S3/2) transition has been generated by two‐photon resonant four‐wave sum frequency mixing in Hg vapor. The quantum yield value for N(4S) formation in the N2O photolysis at 193 nm has been determined to be 2.1 (±0.9) × 10−3. The N(4S) detection technique, which is developed in this study, is very sensitive, and the minimum detection limit is estimated to be 2 × 109 atoms cm−3. Impact of the photolytic N(4S) and NO(X2Π) production from N2O photolysis on stratospheric chemistry has been explored using a one‐dimensional photochemical model, while the fragmentation was not considered in former model calculations. When the N(4S) + NO dissociation channel is considered in the photochemical model, an enhancement of the NOx production rate (up to 3%) is observed, which is followed by a decrease of the steady state O3 concentration throughout the stratosphere.