Photodissociation Dynamics of the Charge-Transfer State of the C₆H₆−I₂ Complex

A pulsed-extraction time-of-flight method was employed to investigate the photodissociation dynamics of the C 6 H 6 −I 2 charge-transfer state. Measurement of the kinetic energy release for the I atom fragments indicates that the charge-transfer state dissociates to a I( 2 P 3/2 ) + I*( 2 P 1/2 ) product state. An anisotropic high-velocity distribution and a Maxwell−Boltzmann distribution with a velocity-dependent spatial anisotropy were observed as distinct components in the product spectra. Rapid dissociation from an oblique complex geometry, with the I 2 bond axis inclined at an angle with respect to the benzene symmetry axis, appears to be responsible for the experimental results. The free I atom recoils away from the complex while the bound I atom interacts strongly with the benzene partner, yielding the different fragment distributions. As a result of charge-transfer excitation, the I 2 is left on the same repulsive excited state that is optically accessed in the uncomplexed molecule, leading to prompt fragmentation. A second mechanism, producing slow I atom fragments, may also contribute to the Maxwell−Boltzmann component. The C 6 H 6 −I 2 complex manifests behavior that can only be understood on the basis of the entire supramolecular complex while other aspects can be rationalized from characteristics of the separated fragments.