H+O2 → +OH+O: Excitation function and absolute reaction cross sections

Abstract

The reaction H + O2 was investigated using translationally excited H atoms from HI photolysis in the range 227-300 nm. An increase in the reaction probability with increasing collision energy up to 175 kJ/mol followed by a decrease at higher E was observed. Rotational distributions were obtained at 240, 250, 254, 262.5, 270, 280, and 290 nm. Absolute reaction cross sections at different collision energies were measured with a calibration method using HNO3 photolysis as a reference: σR (115.7 kJ/mol) = 0.18 ± 0.10 Å2, σR (145.1 kJ/mol) = 0.24 ± 0.13 Å2, σR (171.9 kJ/mol) = 0.65 ± 0.36 Å2, and σR (179.2 kJ/mol) = 0.45 ± 0.25 Å2. The experimental values are compared with cross sections from trajectory calculations on an ab initia H + O 2 potential energy surface. Good agreement was obtained at low and very high energies while in the intermediate range 145-210 kJ/mol the measured cross sections were considerably higher than the calculated ones. Possible reasons for this discrepancy are discussed. © 1992 American Institute of Physics.