Dynamics of the photodissociation of ethyl iodide from the origin of the B band. A slice imaging study

The photodissociation dynamics and stereodynamics of ethyl iodide from the origin of the second absorption B-band have been investigated combining pulsed slicFe imaging with resonance enhanced multiphoton ionization (REMPI) detection of all fragments, I(²P_3/2), I*(²P_1/2) and C₂H₅. The I*(²P_1/2) atom action spectrum recorded as a function of the excitation wavelength permits one to identify and select the 0⁰₀ origin of this band at 201.19 nm (49 704 cm⁻¹). Translational energy distributions and angular distributions for all fragments and semiclassical Dixon's bipolar moments for the C₂H₅ fragment are presented and discussed along with high-level ab initio calculations of potential energy curves as a function of the C–I distance. A predissociative mechanism governs the dynamics where in a first step a bound Rydberg state corresponding to the 5pπ_I → 6s_I transition is populated by the 201.19 nm-photon absorption. A curve crossing with a repulsive state located within the Franck–Condon geometry leads to direct dissociation into the major channel C₂H₅ + I*(²P_1/2). A small amount of I(²P_3/2) atoms is nevertheless observed and presumably attributed to a second curve crossing with a repulsive state from the A-band.