Vibrational Raman spectra of hydrogen deuteride in the critical region

Abstract

Lineshape data have been obtained for the polarized Raman (Q branch) spectrum of HD in the critical region (Tc = 35.91 K). The temperature dependence of the spectrum was investigated in the single phase region along isochores corresponding to the critical density (pc), 0.5pC, and 2.25pc. Spectra of the liquid and vapor were also obtained along the coexistence line down to minimum temperatures of 18.14 K and 31.96 K, respectively. Emphasis is placed on the pronounced variations in lineshape observed on the critical isochore where the behaviour is interpreted in terms of three effects: (i) normal pressure broadening (ii) direct, or pure, vibrational dephasing, and (iii) a specific kind of critical broadening which occurs in the immediate vicinity of the critical point.