A Thermodynamic and Spectroscopic Study of Gaseous Magnesium Oxide

Abstract

Vapor pressure measurements on solid magnesium oxide show that the solid vaporizes mainly into molecular species. Spectroscopic experiments have been conducted and have shown that the known gaseous ¹Σ electronic state of MgO is not the principal vaporizing species. A study of the ultraviolet bands, produced originally by magnesium burning in air, proves the lower electronic level of the molecule involved in this transition is more important than the ¹Σ state of MgO. Within experimental uncertainty the heat of sublimation obtained from vapor pressure measurements agrees with a spectroscopically determined heat of sublimation of the molecule involved in the ultraviolet transition. The ultraviolet bands are shown to originate from a gaseous monomer of MgO. The vapor pressure of MgO at 2200°K is 3.8×10^—4 atmos, and the vapor pressure over MgO reaches 1 atmos at 3040±60°K. The D₀ value for MgO gas is 4.7 ev.