The 266 nm photolysis of ICN: Recoil velocity anisotropies and nascent E,V,R,T excitations for the CN+I(2P3/2) and CN+I(2P1/2) channels

Abstract

We report the detection of nascent CN(X 2Σ+, v″=0) following the 266 nm photodissociation of 300 K ICN, using sub-Doppler resolution laser-induced fluorescence, and polarized photolysis and probe lasers. When monitoring a particular CN internal state, the translational energies of the I+CN and I*+CN channels differ by the iodine spin-orbit splitting 7603 cm−1. This is used to determine the separate contributions from each channel. For I+CN, high N″ are selectively produced, with little population below N″=20 (〈Erot〉 =3300±300 cm−1), whereas the I*+CN channel is associated with a distribution peaked sharply at low N″(〈Erot〉 =355±35 cm−1). It is clear that the low and high N″ derive from linear and bent exit channel geometries, respectively. The spatial anisotropy is high (βI =1.3±0.2; βI* =1.6±0.2) and initial excitation is via a parallel transition(s), probably to a state which begins correlating with I*+CN in the linear configuration. Nascent spin-rotation states (F1 and F2) are also resolved for each channel, and for the case of I+CN, and F1 and F2 populations are quite different. There is very little vibrational excitation (<2%), and the rotational distributions and translational energies of v″=1 and 2 correspond to those of the I+CN channel. Subsequent to initial excitation, both adiabatic and/or nonadiabatic processes can ensure access to potential surfaces not excited directly, and a model is discussed which rationalizes the present experimental results, as well as the known variation of nascent E, V, R, T excitations with the photolysis wavelength.