Collisional Effects in the Absorption Spectra of the Oxygen a Band and Nitric Oxide Fundamental Band

Fourier transform spectroscopy was used to measure pressure broadening coefficients in the absorption spectra of both the oxygen A band and the nitric oxide fundamental band. Oxygen spectra were recorded with O2, N2, CO, CO2, SF6 and noble gas collision partners, while nitric oxide spectra were recorded using noble gas collision partners. Pressure broadening coefficients were determined in the P and R branches for every resolved line for each of the fifteen collision pairs studied. In addition, broadening coefficients and qualitative evidence of line coupling were found for the Q branch of NO + Ar and pressure-induced line shifting coefficients were measured for O2 + Xe. Elastic and inelastic theories of pressure broadening were used to interpret the observed broadening coefficients. The elastic model showed a strong correlation between the magnitude of the coefficients and the polarizability and mass of the perturber. The inelastic contribution to pressure broadening was modeled using both angular-momentum-based and energy-based fitting laws. The ECS-P and EPGL-O laws provided the best fits to the data. The results indicate that the inelastic component is an important contribution to collisional broadening in diatomic molecules and that angular-momentum transfer is a plausible governing mechanism for the inelastic collisions