Dicke Narrowing and Collision Broadening of the Depolarized Rayleigh and <i>S</i>₀(l) Raman Line in the Hydrogen Isotopes and H₂–He, H₂–Ne Mixtures

Abstract

The profile of the depolarized Rayleigh line has been measured in H 2 , D 2 , HD, and in H 2 –He and H 2 –Ne mixtures. In addition the profile of the S 0 (1) rotational Raman line was determined in H 2 and H 2 –He and H 2 –Ne mixtures. Observations were made at room temperature for 90° scattering and over a range of densities varying from about 1 to 100 amagat. Dicke narrowing and collision broadening of the profiles were observed in all cases. A reorientation cross section was calculated from the broadening coefficient of the depolarized Rayleigh line and compared with values obtained from NMR, the Scott effect, and the Senftleben–Beenakker effect. The agreement is satisfactory. From the Dicke narrowing a diffusion constant is extracted and compared with other values. The disagreement is attributed to the inadequacy of the theoretical expression for the contribution of the translational motion to the total profile and to the presence of correlation between the perturbation of the translational and internal molecular motion.