Solubilities of hydrogen and deuterium gases in water and their isotope fractionation factor

Abstract

Solubilities of deuterium gas in water were measured at 5° intervals from 278 to 303°K with an overall precision of about 0.4%. Thermodynamic functions for the solution process were calculated for deuterium gas and compared with the corresponding quantities for hydrogen gas based on the reported data of Crozier and Yamamoto. Henry's law constantsk, obtained at different temperaturesT, were fitted to an equation of the form $$R ln ({1 \mathord{\left/ {\vphantom {1 k}} \right. \kern-\nulldelimiterspace} k}) = A + {B \mathord{\left/ {\vphantom {B {T + }}} \right. \kern-\nulldelimiterspace} {T + }}C ln T + DT$$ Isotope fractionation factors α for the D2/H2 system were obtained with careful error estimates. Compared at the same temperature, D2 gas is more soluble in water than H2 gas, showing a “normal” isotope effect, and the value of α decreases from 1.086 (±0.005) at 278°K to 1.065 (±0.006) at 303°K. The large isotope effect may be attributed, at least partly, to the difference in the zero-point energies between H2 and D2 molecules when they execute oscillatory motion in a solvent cage.