Rydberg–valence interactions in CH2Cl\CH2¿Cl photodissociation: Dependence of absorption probability on ground state vibrational excitation

A strong enhancement of absorption to the lowest A1 state is observed for vibrationally excited chloromethyl radicals. It is demonstrated that this enhancement is due to a significant increase in both electronic and vibrational Franck–Condon factors. Electronic structure calculations of potential energy surfaces ~PESs! and transition dipole moments for the ground and the two lowest excited states of A1 symmetry, the 1 A1 valence and 2 A1 Rydberg states, reveal the origin of this effect. The shelflike shape of the 1 A1 PES in the Franck–Condon region and the strong dependence of the electronic transition dipole moment on C–Cl distance are responsible for the enhancement. Analysis of the shape of the electron density distribution demonstrates that Rydberg–valence interaction in the two lowest excited states causes the changes in the shape of PESs and transition dipoles with C–Cl distance. © 2003 American Institute of Physics. @DOI: 10.1063/1.1568076#