A measurement of the vibrational band strength for the ν3 band of the HO2 radical

Abstract

The HO2 radicals generated in a discharge-flow system have been observed with tunable diode laser absorption in the P branch of the ν3 vibrational band at 1080 cm−1. The observed line positions agree within (2 to 5)×10−3 cm−1 with those calculated from the molecular constants for the ν3 band obtained from a previous study using laser magnetic resonance spectroscopy. The band strength has been determined by observing line center absorptions when HO2 is produced in the reaction F+H2O2→HO2+HF (k1) with a measured concentration of atomic fluorine and excess hydrogen peroxide. F-atom concentrations are measured by diode laser absorption of the spin-orbit transition at 404 cm−1. The analysis accounts for HO2 losses due to the reactions of HO2+HO2→H2O2+O2 (k3) and F+HO2→HF+O2 (k4). The experimental data are consistent with a value of k3=(1.6±0.3)×10−12 cm3 s−1 and a ratio k4/k1=1.0±0.4. The line strength for the 615←716 F1 transition is 2.9×10−21 cm2 molecule−1 cm−1 which corresponds to a ν3 band strength of 35±9 cm−2 (STP atm)−1. This value is a factor of 1.6 to 6 lower than previous ab initio calculations.