Predissociation lifetimes in two excited electronic states of HCN and DCN

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Abstract
Through computer simulation of predissociated absorption bands of HCN, DCN, D13CN, and DC15N, between 54 563 and 65 644 cm−1, average linewidths and lifetimes of representative upper-state levels are derived. Lifetimes of DC15N vary from 115 to 0.66 ps for à 1A″-state levels. Each of the three vibrations (a′) is found to couple efficiently the à state to a second 1A″ state, allowing radiationless transitions from the à state, and subsequent dissociation. The lifetime of HCN in the zero level of the C̃ 1A′ state is 0.95 ps, a value comparable to those of neighboring Ã-state levels; therefore the dominant predissociation mechanism for the C̃ state is assumed to be coupling of the C̃ and à electronic states by rotation, around one or both of the in-plane inertial axes.