Reaction of well-characterized vibrational states prepared in the region of three quanta of N-H stretching excitation explores how vibrations with different components along the reaction coordinate influence the bimolecular reaction of Cl atoms with isocyanic acid (HNCO) to form HCl and NCO. Near prolate symmetric top states corresponding to different amounts of a-axis rotation are well separated in energy, and perturbations by background states make each of the eigenstates a different mixture of zero-order states. Molecules in the essentially unperturbed K=1 and 4 states, which are nearly pure 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 frequency vibrations react only half as well. Detailed analysis of resolved, perturbed 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 quanta of other vibrations, reacts only 10% as well as the pure N-H stretch zero-order state. Ab initio calculations suggest that bending excitation alters the interaction potential to reduce the fraction of reactive collisions.