Combination Reactions of Imino Radicals in the Flash Photolysis of Isocyanic Acid

The flash photolysis of HNCO vapor yielded CO, N₂, and H₂ in a ratio of 1/0.42/0.27, independent of HNCO pressure (7–40 mm) and flash energy (17–1150 J). From the mass balance, production of ammonia was implied; the stoichiometry was described approximately by 12 $\mathrm{HNCO}\text{=12}\mathrm{CO}\text{+5}{\mathrm{N}}_2\text{+3}{\mathrm{H}}_2\text{+2}{\mathrm{NH}}_3$ . It was concluded that the reaction 2NH→N₂H₂ was much more important than 2NH→N₂+H₂, with the observed stoichiometry largely determined by the subsequent decomposition of N₂H₂. The addition of ethylene or propane reduced the yield of CO (by competitive absorption of light), and reduced the value of N₂/CO, apparently for the most part by interfering in the decomposition of N₂H₂ rather than by reacting with NH radicals. The effect on the hydrogen yield was complicated by the production of hydrogen by photolysis of ethylene and propane; in the HNCO—propane system, however, extra hydrogen definitely was produced, probably by the reaction of NH with propane.