Uranium Monosulfide. II. Mass Spectrometric Study of Its Vaporization

A study of the vapor effusing from a tungsten effusion cell containing uranium monosulfide has been performed with the aid of a time‐of‐flight mass spectrometer. Between 1700° and 2150°C uranium monosulfide vaporizes predominantly according to the reactions $$\mathrm{US}\mathrm{(s)=}\mathrm{US}\mathrm{(g),}$$ and $$\mathrm{US}\mathrm{(s)=}\mathrm{U}\mathrm{(g)+}\mathrm{S}\mathrm{(g),}$$ and to a detectable extent at 2100°C and above by the reaction $$2\mathrm{US}\mathrm{(s)=}{\mathrm{US}}_2\mathrm{(g)+}\mathrm{U}\mathrm{(g).}$$ Least squares treatment of the ion current ratio I_US⁺/I_U⁺ as a function of temperature between 1885° and 2130°C yields the relationship ΔH_T°(I) —[ΔH_T°(II)/2]=14.6±2.4 kcal/mole, where the error is estimated. In the presence of very small amounts of oxygen in the solid monosulfide the vapor species UO and UOS are found. A faint peak in the spectrum at mass 264 is suspected to have been due to ThS⁺.