The spectroscopy, photophysics and photodissociation dynamics of jet-cooled CF3NO[Ã(n,π*)]

Abstract

The LIF excitation spectrum of jet-cooled CF₃NO in the visible has been reinterpreted and the torsional structure has been analysed in detail yielding a V^′₃ barrier to internal rotation of 601.5 cm^–1. The predissociation dynamics of jet-cooled CF₃NO(ùA″) have been re-examined using single vibranic level excitation with a pulsed dye laser and fluorescence decay measurements. Quantum beats and biexponential fluorescence decay behaviour indicate that all levels of the S₁(n,π*) state are coupled to levels of the T₁ state. The NO photofragment yield spectrum indicates that vibrations with CNO bending character act as promoting modes for the radiationless transition out of S₁. Rotational distributions of the nascent NO photoproduct have been characterised in detail and are found to deviate little from statistical distributions, but the F₂/F₁ spin-orbit branching ratio is very non-statistical, favouring the lower ²Π_1/2 state of NO. The threshold for the dissociation of CF₃NO(D₀) and the electronic origin of the Ãâ†�X transition (T⁰₀) have been redetermined and are found to coincide (D₀= 13 980 ± 60 cm^–1, T⁰₀= 13 929.7 cm^–1). Intersystem crossing and the T₁ state are found to be important in the predissociation dynamics of all but the lowest Ã-state levels.