FAST BEAM STUDIES OF NCO FREE-RADICAL PHOTODISSOCIATION

The spectroscopy and dissociation dynamics of the NCO radical have been investigated by applying fast radical beam photodissociation spectroscopy to the B2PI <-- X2PI electronic transition. Measurements of the photodissociation cross section as a function of dissociation wavelength show that even the lowest vibrational levels of the B2PI state predissociate. Analysis of fragment kinetic energy release reveals that the spin-forbidden N (4S) + CO(1SIGMA+) products are produced exclusively until 20.3 kcal/mol above the origin, at which point, the spin-allowed N(2D) + CO product channel becomes energetically accessible. The spin-allowed channel dominates above this threshold. By determining the location of this threshold, we obtain a new DELTAH(f)0 for NCO of 30.5 +/- 1 kcal/mol, several kcal/mol lower than the previously accepted value.