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( ² P _3/2 ), I*( ² P _1/2 ) and C ₂ H ₅ . The I*( ² P _1/2 ) atom action spectrum recorded as a function of the excitation wavelength permits one to identify and select the 0 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 C ₂ H ₅ 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 C ₂ H ₅ + I*( ² P _1/2 ). A small amount of I( ² P _3/2 ) atoms is nevertheless observed and presumably attributed to a second curve crossing with a repulsive state from the A-band.