Study of collisional deactivation of O2(b1Σg+) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

Collisional deactivation of O 2 ( b 1 Σ g + ) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H 2 /O 2 mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b 1 Σ g + state of O 2 molecules deactivation rates are measured in a 4.3 vol % H 2 mixture at the number density of 2 amg in the temperature range 291–850 K. The physical deactivation is shown to dominate in the collisions of H 2 with O 2 ( b 1 Σ g + ) and O 2 ( a 1 Δ g ) up to temperatures of 780–790 K at time delays up to 10 μs after the excitation pulse. The parameters of the obtained temperature dependence of the ( b 1 Σ g + state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200–400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H 2 O molecules which appear as the mixture, as the result of the dark gross reaction with O 2 molecules in the ground state, O 2 + 2H 2 → 2H 2 O. The measurements show that this reaction results in complete transformation of H 2 into H 2 O at temperatures of 790–810 K.