Accurate study of the two lowest singlet states of HN_3: Stationary structures and energetics at the MRCI complete basis set limit

摘要

The two lowest singlet potential energy surfaces of the hydrazoic acid are explored using high-level quantum chemistry calculations, revealing isomeric forms, transition states, and a new path for the nitrogen ring-closing mechanism in the ground state. The reaction of cyc-N_3 with hydrogen is shown to proceed through a barrierless path that dissociates to N_2 + NH(1Δ) without reaching the HN_3 global minimum. Several intersections between the two states are localized for both N _3 isomers near the N_3 + H dissociation. The energies of stationary structures and dissociation asymptotes are obtained with the multireference configuration interaction method at the complete basis set limit. A comparison with recent experimental data regarding the H-N_3 bond strength and the dissociation barrier in the excited state shows that the present results are of chemical accuracy (～1 kcal mol-1).