Gas phase generation of O 2( +Δ g) at atmospheric pressure by direct laser excitation

Abstract

O 2( 1Δ g) was generated in the gas phase at atmospheric pressure by direct laser excitation. A Holobeam model 255 Nd—YAG laser with an output at 1065 nm was used to achieve the transition O 2( 3Σ g −, v = 0) → O 2( 1Δ g, v = 1) The mean lifetime τ of the resulting excited oxygen species in the gas phase at atmospheric pressure was measured to be 0.124 ± 0.012 s. This corresponds to a bimolecular rate constant k 2 for the overall reaction O 2( 1Δ g, v = 1) + O 2( 3Σ g −) → 2O 2( 3Σ g −) of (3.3 ± 0.4) × 10 −19 molecule −1 cm 3 s −1, a factor of 10 below the currently accepted value for ground state oxygen deactivation of singlet oxygen. Possible reasons for this difference are discussed.