Mass Spectrometric Study of Ferrous Chloride Vapor

Mass spectrometric studies of the vaporization process of ferrous chloride show that the major vapor species is monomeric FeCl2(g). A small concentration of Fe2Cl4(g) is present in the vapor at low temperatures. The ratio of dimer to monomer concentration increases rapidly with temperature showing that at the melting point of FeCl2(s), the equilibrium vapor consists of about 25% dimer. Thermodynamic treatment of ion current data yields for the reaction 2FeCl2(s)=Fe2Cl4(g),ΔH640∘K∘=56±3 kcal/mole of dimer and for the reactionFe2Cl4(g)=2FeCl2(g),ΔH640∘K∘=32±3 kcal/mole of dimer.