J . Phys. Chem. 1988, 92, 5580-5593
5580
the hydrogen atom as occurs in O(lD) + HN,. Since production of "(A) as observed in these experiments is exothermic by only 7 kcal mol-I, the branching fraction to this excited state is likely to be small. Indeed, spin conservation would predict the formation of excited singlet states of N H (i.e., alA or b'B+) in reaction 2. It is not surprising that emission from these states was not observed in our experiments, given their very long radiative lifetimes." The absence of N C O radicals in the reaction medium argues that process 2 above is the dominant route for O(lD) reaction with HNCO. In order to quantify this result, experiments were performed to determine the detection limit of the N C O LIF experiments. For this purpose, N C O radicals were produced by admission of a known flow of H N C O to excess F atoms (from a discharge through CF,/Ar) in a discharge-flow assembly which was affixed to the photolysis cell. This reactionI2 rapidly produces H F NCO, and LIF from the N C O radicals was readily detected. Assuming that H N C O is converted to N C O with unit efficiency, the minimum density of N C O detectable by the LIF experiment was determined to be
