Mass-Spectrometric Study of the Magnesium Halides

The vapor composition of the four magnesium halides has been studied by mass analyzing the vapor effusing from a Knudsen cell. In each instance, ∼1% dimer and 0.01% trimer were observed. Heats of sublimation have been measured by second- and third-law methods. The discrepancy between the two methods varies from 2 kcal/mole for MgI2 to 5 kcal/mole for MgF2, with the third-law method giving consistently lower values. The experimental heats of ionization of the monomers are in fair agreement with calculations based on an ionic model. The fragmentation pattern of the fluoride is anomalous as it is with the alkali-halide systems. The measured relative ionization cross sections are in surprisingly good agreement with the relative electric polarizabilities of the anions.