Mass Spectrum of Lithium Iodide

Abstract

The mass spectrum of lithium‐iodide vapor produced from salt heated in an oven in the ion source of an analytical mass spectrometer was investigated as a function of oven temperature. Evidence was obtained for the existence in the vapor of both monomer and dimer. Partial heats of sublimation to monomer and dimer at 0°K were found to be 44.9±0.7 and 45.5±2 kcal respectively. The heat of dissociation of (LiI)₂ into gaseous monomers was found to be 44.4±2.2 kcal. The partial heat of sublimation of monomer was used with supplementary thermochemical data to obtain values for the lattice energy and the heat of dissociation of the diatomic molecule. Appearance potentials for the major ions in the spectrum where determined. Upper limits for the energy of dissociation of the gaseous diatomic molecule were derived from the appearance potentials of Li⁺ and I⁺ which were slightly higher than the thermochemical value.