Full-dimensional potential energy surface for the photodissociation of HNCO via its S1 band

Abstract

A full-dimensional potential energy surface (PES) for the first excited state S₁(¹A′′) of HNCO has been built up by the neural network method based on more than 36 000 ab initio points, which were calculated at the multireference configuration interaction level with Davidson correction using the augmented correlation consistent polarized valence triple zeta basis set. It was found that two minima, namely, trans and cis isomers of HNCO, and another seven stationary points exist on the S₁ PES for the two dissociation pathways: HNCO(S₁) → H + NCO/NH + CO. Particularly, a new out-of-plane transition state between the two minima was found in this work, thanks to including all the degree of freedoms for this system. The adiabatic excitation energy of the S₁(¹A′′) ← S₀(¹A′) transition and dissociation energies D₀(HNCO → H + NCO) and D₀((HNCO →NH(a¹Δ) + CO) calculated on the PES are in good agreement with experimental results. In addition, based on the newly constructed S₁ PES, the percentage of products H + NCO in the photodissociation of HNCO(S₁) was obtained by a quasi-classical trajectory method at the photon wavelengths ranging from 190 to 225 nm, which is in reasonably good agreement with earlier theoretical and experimental results. For the dissociation lifetimes of the trajectories, they were calculated to be less than 5 ps, which is also consistent with experimental observations.