Equilibrium Composition of Selenium Vapor; the Thermodynamics of the Vaporization of HgSe, CdSe, and SrSe

The vapor compositions of SrSe, CdSe, HgSe, hexagonal selenium, α-monoclinic selenium, and some mixed sulfur—selenium crystals have been studied by mass-spectrometric analysis. Dissociation energies of Se2 (71.2±2 kcal/mole) and SrSe (59.1±3 kcal/mole) were obtained. The heats and free energies of formation of the various Sen molecular species detected in the vapor are also given. There is no significant difference between the vaporization behavior of the two Se allotropes. Mixed sulfur—selenium molecules form very slowly at room temperature, but they form more readily at higher temperature, and quenching to room temperature retains the mixed configurations.