Vapour pressure of liquid deuterium sulphide

The vapour pressure of liquid D2S and the difference between the vapour pressures of liquid H2S and D2S have been measured at 22 temperatures in the T = (193 to 230) K range. The vapour pressure data, corrected to 100 per cent isotopic purity, have been fitted with the equation: (T/K). lnr = -29.385 +/- 5298.6 .(K/T) +/- 0.02557 .(T/K), where r is the vapour pressure ratio between the isotopic species, r = p(H2S)/p(D2S). This system exhibits a crossover point (r = 1 at T approximate to 224 K) in the vapour pressure isotope effect (VPIE). The VPIE is normal in the lower temperature range and inverse at higher temperatures. Comparisons with both experimental and theoretical data from other authors confirm the validity of the fitted equation as a way to describe the vapour pressure isotope effect of (dihydrogen sulphide + dideuterium sulphide) in the liquid phase. (C) 1996 Academic Press Limited