High-resolution line broadening and collisional studies in CO2using nonlinear spectroscopic techniques

High-resolution line-broadening studies have been made of C${\mathrm{O}}_2$ in collision with a wide variety of foreign gas perturbers. These measurements have been made by observation of the narrow saturated resonance in the 4.3-μm fluorescence emitted from a low-pressure C${\mathrm{O}}_2$ gas which is subjected to a saturating standing-wave electric field from a C${\mathrm{O}}_2$ oscillator operating on a 9.6- or 10.6-μm transition. The collision partners which have been investigated are C${\mathrm{O}}_2$, ${\mathrm{N}}_2$O, ${\mathrm{N}}_2$, NO, CO, ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, Ne, Ar, Kr, Xe, N${\mathrm{H}}_3$, and C${\mathrm{H}}_4$. A semiclassical theory of the 4.3-μm saturated resonance is developed which accounts for the effects of phase-interrupting collisions, beam transit time, and optical intensity. The observation of a previously unobserved downward curvature of the C${\mathrm{O}}_2$ linewidth data at low pressure is attributed to the influence of the transit-time effect. The experimentally determined pressure-broadening coefficients include the important correction for the contribution of power broadening. These power-corrected results for C${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ have been used to predict successfully the observed gain characteristics of high-pressure (> 1 atm) C${\mathrm{O}}_2$ amplifiers, as observed in other studies. We have also appraised our observed broadening coefficients in the context of the pressure-broadening theory developed by Murphy and Boggs in order to characterize quantitatively the intermolecular interactions. The comparison of theory and experiment indicates the need for an explicit incorporation of vibration perturbations in the theoretical analysis, particularly when vibrational resonance is present.