A Spectrometric Technique for Monitoring [O 2 ( a 1 Δ g )] in the Gas Phase

Abstract

The reaction of chlorine with alkaline hydrogen peroxide has been used to produce O₂(a¹ Δ _g ) in a fast flow system at partial pressures up to about 0.5 Torr, and total pressures (mostly argon) in the range 0.8–2.5 Torr. Absolute concentrations of O₂(a¹ Δ _g ) were determined from the intensity of absorption of hydrogen emission lines in the vacuum-UV at 144.095 and 148.66 nm, for which the cross sections are known. The intensity of the O₂ (a → X) transition at 1270 nm, monitored simultaneously with a simple germanium detector, was found to vary linearly with [O₂(a¹ Δ _g )], as expected. The germanium detector was calibrated at 1270 nm with a readily reproducible standard, the air afterglow continuum due to NO₂* at defined concentrations of O(³P) and NO. The ratio of k_a for O₂(a) k_a O ₂ (X) + hv_t to k_c for O + NO k_c NO₂ + hv, is (1.4 ± 0.2) × 10⁻⁷ mol L⁻¹ at 1270 nm.