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(P-2(3/2)), I*(P-2(1/2)) and C2H5. The I*(P-2(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 5p pi(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*(P-2(1/2)). A small amount of I(P-2(3/2)) atoms is nevertheless observed and presumably attributed to a second curve crossing with a repulsive state from the A-band.