AbstractSome recent examples of reactions proceeding both in the gas phase and in solution have been investigated to determine their kinetics and mechanisms. The ratio of the corresponding rate constants, kGand kL, of the elementary processes studied has been found to be about unity for unimolecular reactions and between 1 and 10 for bimolecular reactions. The mechanisms, overall rates, rate constants, and activation energies have been determined for the homogeneous gas reaction NOCl + Cl2O = NO2Cl + Cl2and the reaction NOCl + N2O5= NO2Cl + 2 NO2, carried out in C2F3Cl3.