Multiphoton dissociation dynamics of the indenyl radical at 248 nm and 193 nm.

Photofragment translational spectroscopy is used to investigate the unimolecular photodissociation of the indenyl radical (CH). CH radicals are generated by photodetachment of CH anions and are dissociated at 248 nm (5.00 eV) and 193 nm (6.42 eV). The following product channels are definitively observed at both wavelengths: CH + CH, CH + CH + CH, and CH + CH + CH. The three-body product channels are energetically inaccessible from single photon excitation at either dissociation wavelength. This observation, in combination with calculated dissociation rates and laser power studies, implies that all dissociation seen in this experiment occurs exclusively through multiphoton processes in which the initial CH radical absorbs two photons sequentially prior to dissociation to two or three fragments. The corresponding translational energy distributions for each product channel peak well below the maximum available energy for two photons and exhibit similar behavior regardless of dissociation wavelength. These results suggest that all products are formed by internal conversion to the ground electronic state, followed by dissociation.