Speed-Dependent Inhomogeneities in Collision-Broadened H2 Vibrational Transitions

Abstract

Publisher Summary The collisional broadening of an isolated rotation–vibration transition of gas is considered to be in the impact regime when the collisional width is small compared to the inverse of the collision duration and large compared to the Doppler width. The collisional width and shift have no significant dependence on relative molecular speeds. Such conditions have been shown to produce Lorentz line profiles. This chapter presents the observations of inhomogeneous broadening in the vibrational line profiles of H2 perturbed by a heavy collision partner, at densities normally considered to be in the impact regime. At densities up to 27 amagat, non-Lorentzian, asymmetric features are observed in Raman Q-branch transitions of H2 diluted in a heavy perturber gas. These measurements are compared with an inhomogeneous line-profile model based on strong speed dependences in the collisional shift cross sections. Quantitative agreement is obtained only when spectral line narrowing resulting from speed-changing collisions is included.