Mixtures of CH212 and ClN3 are photolyzed a t 193 nm to produce iodine atoms and NCl(alA), respectively. The collisional excitation of the iodine atoms to the 52Pl/2 state is readily observed from the time profile of chemiluminescence from this species. From a steady-state treatment of the intensities, the rate constant for the specific energy-transfer process (i.e., the excitation of the 12P1/2 state) is determined to be k = (1.8 f 0.3) X lo-" cm3 s-I. The branching fraction for production of 12Pl/2 in the overall quenching of NCl(alA) by iodine atoms has a lower limit of 0.25. Excited I2P1/2 is quenched by ClN3 with a rate constant kQ = (2.0 f 0.3) X lo-" cm3 s-I. From these rate constants and comparison of the I2P1/2 and NCl(a'A) time profiles, it is inferred that energy transfer from 12P1,2 to ClN3 regenerates both IzP3/2 and NCl(alA), such that cycling of the iodine atoms between the 2P1/2 and 2P3/2 states serves to drain the energy stored in the azide.

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