Hydrogen–Deuterium Self-Exchange in Hydrogen Sulfide and Hydrogen Selenide as Studied with a Pulsed-Molecular-Beam Quadrupole Mass Filter

The equilibrium constants for hydrogen–deuterium self-exchange in hydrogen sulfide and hydrogen selenide have been studied over a wide range of deuterium atom percent using a pulsed-molecular-beam quadrupole mass filter. KHDS was found to be 3.88 ± 0.03 at 24.0 ± 0.4°C and KHDSe was found to be 3.92 ± 0.04 at 22 ± 1°C. The experimental results agree with calculations from spectroscopic data to within 1%. It is shown that equilibrium constants for self-exchange reactions in systems where two hydrogenic species are exchanged tend toward the geometric mean value of K = 4 in the series H2O:H2S:H2Se as expected from theory.