Theoretical studies on photolysis and pyrolysis of isocyanic acid

Photolysis and pyrolysis of HNCO have been investigated with the ab initio molecular orbital method. The geometries are optimized with the MP2 gradient technique. The matrix elements of the spin-orbit are calculated and the results show that this interaction is the important mechanism for ground-state dissociation into the products NH and CO at high temperature. The excited vibrational levels of the 1A″ electronic state probably dissociate directly into the products via the transition state TS(1A″). A simple impulse model, combined with optimized structure of the TS(1A″), can predict the nascent-fragments energy distributions.