The distribution of vibrational states which are excited by resonant radiation and deactivated by a relaxation process is strongly influenced by the anharmonicity of the molecule and the red shifting of the resonant frequency. Steady‐state distribution curves are calculated for the BCl3molecule, the &ngr;3mode of which is resonant to CO2laser light. A flux of states is defined for these distribution functions which is recognized as the rate for photochemical reactions. Some results are given for photodissociation, which show that proper detuning of the light can increase the rate of photodissociation by several orders of magnitude.