Using stretching and bending vibrations to direct the reaction of Cl atomswith isocyanic acid (HNCO)

Reaction of well-characterized vibrational states prepared in the region of three quanta of N-H stretching excitation explores how vibrations with dif ferent components along the reaction coordinate influence the bimolecular r eaction of Cl atoms with isocyanic acid (HNCO) to form HCl and NCO. Near pr olate symmetric top states corresponding to different amounts of a-axis rot ation are well separated in energy, and perturbations by background states make each of the eigenstates a different mixture of zero-order states. Mole cules in the essentially unperturbed K=1 and 4 states, which are nearly pur e N-H stretching excitation, react efficiently, but those in the perturbed states, K=0, 2, and 3, which are a mixture of N-H stretching and lower freq uency vibrations react only half as well. Detailed analysis of resolved, pe rturbed eigenstates for J=6 and 7 of K=3 reveals the relative reactivity of the two interacting zero-order states. The less reactive zero-order state, which most likely contains only two quanta of N-H stretch and several quan ta of other vibrations, reacts only 10% as well as the pure N-H stretch zer o-order state. Ab initio calculations suggest that bending excitation alter s the interaction potential to reduce the fraction of reactive collisions. (C) 1999 American Institute of Physics. [S0021-9606(99)01337-9].