Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of the Free Radical NCO

The free radical NCO is stabilized in sufficient concentration for direct infrared and ultraviolet spectroscopic identification upon vacuum-ultraviolet photolysis of HNCO suspended in various matrix materials at 4° and at 14°K. Observations on the B(2Π)—X(2Π) electronic transition of NCO have been extended to shorter wavelengths than those previously reported. Isotopically substituted NCO has been prepared in supplementary experiments involving the vacuum-ultraviolet photolysis of CO:HN3 and Ar:HCN:N2O samples, as well as by the mercury arc photolysis of matrix-isolated samples of NO+N3CN. The three vibrational fundamentals of ground-state NCO appear at 487, 1275, and 1933 cm−1 in an Ar matrix. The values obtained for the stretching force constants suggest that the carbon—oxygen bond may be somewhat stronger than the carbon—nitrogen bond. There is an appreciable positive stretching-interaction force constant. NCO is found to photolyze when subjected to radiation of wavelength near 2537 Å, leading to the production of N+CO. Reactions occurring in the various systems investigated are discussed.