Matrix-Isolation Study of the Photolysis of Cyanogen Azide. II. The Symmetric Stretching Fundamental of the Free Radical NCN

The photolysis of Ar:N3CN samples at 14°K with the full light of a cadmium arc has been found to permit complete conversion of the cyanogen azide to the free radical NCN, plus molecular nitrogen. At the high concentration of NCN thus achieved, a weak absorption appears at 2672 cm−1. The photolytic behavior of this feature and its shifts upon isotopic substitution support its assignment as the combination band (ν1+ν3) of NCN, permitting deduction of a value of 1197 cm−1 for ν1 of this species. The thermodynamic properties of NCN have been revised in accord with this assignment. The carbon—nitrogen stretching force constant approaches a value characteristic of a doubly bonded species, and the stretching interaction constant is relatively large and positive. Cyanogen azide photolyzes in both its 2750- and its 2200-Å absorption regions to produce NCN+N2. However, NCN itself photolyzes when subjected to radiation near 2500 Å, producing carbon atoms in the 3P state, which, in turn, may react with N2 to form the free radical CNN.