Mass spectrometer analyses of equilibrium vapors over molten AgCl between 772 deg and 1,014 deg K, indicate the existence of the vapor molecule Ag3Cl2 in addition to the monomer and trimer. The data predict the monomer concentration to increase with increasing temperature. "Second law" heats of vaporization for the three vapor species are 41.4 +/- 2.2 Kcal mole-1 for AgCl, 33.6 +/- 3.2 Kcal mole -1 for Ag3Cl2, and 26.9 +/- 2.7 Kcal mole-1 for Ag3Cl3. A value of -97.3 +/- 7.1 Kcal mole-1 is derived for the heat of trimerization. A dissociation energy of 3.4 +/- 0.4 eV (78.2 +/- 9.2 Kcal mole-1) for the monomer vapor molecule and a dissociation energy of 0.7 eV (16.1 Kcal mole-1) for the molecular monomer ion is calculated from the appearance-potential data.