Equilibrium constants of hydrogen--deuterium--tritium self-exchange reactions in water vapor as studied with a pulsed molecular-beam quadrupole mass filter

We measured the equilibrium constants KHDO = P2HDO/PH2O⋅PD2O, KHTO = P2HTO/PH2O⋅PT2O, and KDTO = P2DTO/PD2O⋅PT2O at 295.6°K (22.4°C), assuming the mass spectrometric sensitivities of the three species cancel in each expression of the equilibrium constant. The results obtained were KHDO = 3.82±0.05, KHTO = 3.66±0.06, and KDTO = 3.99±0.07. These values agreed with the current theoretical values of KHDO = 3.84, KHTO = 3.69, and KDTO = 3.97 at the same temperature. We discuss the discrepancy of the present value of KHDO as compared with previous experimental determinations, and we conclude that a direct measurement of the mass spectrometric sensitivity ratio for KHDO is still necessary to resolve the disagreement. We prepared the water mixtures that contained tritium by reacting the appropriate hydrogenic gases with oxygen over a platinum sponge catalyst.