Speed-dependent broadening of the [formula omitted] fine-structure lines

Abstract

Pressure broadening of the molecular oxygen fine-structure lines near 60 GHz was experimentally reexamined in the range of rotational quantum numbers up to N=39, in the pure gas at room temperature. The analysis of a representative set of individual line profiles with N varying from 1 to 21 included the speed dependence of collisional relaxation, which affects absorption by 0.25–0.5% of maximum at low pressures. The ratio of the two speed-dependence parameters γ0 and γ2 exhibits no notable variation with N. Obtained data are compared with similar parameters of other oxygen bands in the near-infrared and visible spectral ranges. Assuming similar speed dependence in air as for pure oxygen, we find that at 1-atm pressure, the impact of introducing speed-dependent line mixing and broadening coefficients into a model for the atmospheric oxygen 60-GHz band is 0.05–0.1% of maximum absorption, much smaller than the influence of either first- or second-order speed-independent line mixing.