Collisional effects in the stimulated Raman Q branch of O2 and O2–N2

Abstract

The fundamental isotropic Raman Q branch of oxygen at pressures up to 2 atm and for temperatures between 295 and 1350 K has been recorded using stimulated Raman gain spectroscopy (SRGS) for collisions with oxygen and nitrogen. The line broadening and line shifting coefficients have been determined for several rotational quantum numbers (up to N=55 at 1350 K). The temperature dependence of these coefficients has also been studied for most of the rotational lines. The line parameters (widths and shifts) have been then calculated a priori through a semiclassical model. A good agreement between experimental and theoretical data has been observed. Another theoretical approach based on fitting and scaling law has been used to calculate the line broadening coefficients. It is shown that a modified exponential energy gap model (MEG) and an energy corrected sudden law (ECS) for the state-to-state rotationally inelastic rates, account for the rotational and temperature dependences of the observed linewidths. With regard to the energy corrected sudden law, the best results are obtained when the basis rate constants are modeled with a hybrid exponential-power fitting law (EP). The line broadening and shifting coefficients of the oxygen–nitrogen mixture are very close to those found for pure oxygen.