The thermal exchange of chlorine between ** f and liquid ** f is readily measurable at temperatures in the range of 180 ` and above. The photochemical exchange occurs with a quantum yield of the order of unity in the liquid phase at 65 ` using light absorbed only by the ** f. In the gas phase, with ** f of ** f and ** f of ** f, quantum yields of the order of ** f have been observed at 85 `. Despite extensive attempts to obtain highly pure reagents, serious difficulty was experienced in obtaining reproducible rates of reaction. It appears possible to set a lower limit of about ** f for the activation energy of the abstraction of a chlorine atom from a carbon tetrachloride molecule by a chlorine atom to form ** f radical. The rate of the gas phase exchange reaction appears to be proportional to the first power of the absorbed light intensity indicating that the radical intermediates are removed at the walls or by reaction with an impurity rather than by bimolecular radical combination reactions.

Because of the simplicity of the molecules, isotopic exchange reactions between elemental halogens and the corresponding carbon tetrahalides would appear to offer particularly fruitful possibilities for obtaining unambiguous basic kinetic data. It would appear that it should be possible to determine unique mechanisms for the thermal and photochemical reactions in both the liquid and gas phases and to determine values for activation energies of some of the intermediate reactions of atoms and free radicals, as well as information on the heat of dissociation of the carbon halogen bond. The reaction of chlorine with carbon tetrachloride seemed particularly suited for such studies. It should be possible to prepare very pure chlorine by oxidation of inorganic chlorides on a vacuum system followed by multiple distillation of the liquid. It should be possible to free carbon tetrachloride of any interfering substances by the usual purification methods followed by prechlorination prior to addition of radioactive chlorine. Furthermore, the exchange would not be expected to be sensitive to trace amounts of impurities because it would not be apt to be a chain reaction since the activation energy for abstraction of chlorine by a chlorine atom would be expected to be too high; also it would be expected that ** f would compete very effectively with any impurities as a scavenger for ** f radicals. Contrary to these expectations we have found it impossible to obtain the degree of reproducibility one would wish, even with extensive efforts to prepare especially pure reagents. We are reporting these investigations here briefly because of their relevancy to problems of the study of apparently simple exchange reactions of chlorine and because the results furnish some information on the activation energy for abstraction of chlorine atoms from carbon tetrachloride.