The photodissociation of HNCO in the S-1 band: A five-dimensional classical trajectory study

We present a classical trajectory study of the photodissociation of HNCO in the S-1 electronic state using a five-dimensional potential energy surface with all atoms confined to a plane. The potential energy surface has been determined by ab initio calculations (multi-reference configuration-interac tion method, triple-zeta basis set). Because any coupling to other electron ic states is neglected in our calculations, direct comparison with experime ntal data is limited and basically restricted to energies well above the HN (a (1)Delta)+CO channel. Nevertheless, some aspects are described in a real istic way and help to interpret experimental results. In particular, the ca lculated vibrational-rotational state distributions of the diatomic fragmen ts are in good agreement with the measured ones. Moreover, our calculations support the most recently published data on the H-atom quantum yield for p hotolysis with 193-nm photons. It is found that pre-excitation of the HN st retching mode by several quanta significantly enhances the lifetime with re spect to breaking the NC bond, which may partly explain the drastic increas e of the H-atom quantum yield in the vibrationally mediated photodissociati on. (C) 1999 American Institute of Physics. [S0021-9606(99)02137-6].