The thermodynamic functionsCp0,S0, —(F0—E00)/T,and (H0—E00)/Tof the six diatomic interhalogens, chlorine monofluoride, bromine monofluoride, iodine monofluoride, bromine monochloride, iodine monochloride, and iodine monobromide, have been evaluated as a function of temperature from 298.16°K to 2000°K by the application of statistical methods. These results have been combined with newly evaluated properties of the fluorine, chlorine, bromine, and iodine atoms and molecules to yield the heats and free energies of dissociation and dissociation constants for the equilibria between the interhalogens and their molecular and atomic dissociation products. The calculations are based on available experimental spectroscopic constants with the exception of the anharmonicity term and internuclear distance for bromine chloride and of the internuclear distances in iodine fluoride and iodine bromide. These quantities are estimated empirically.