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 (2)A(1) 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 A(1) symmetry, the 1 (2)A(1) valence and 2(2)A(1) Rydberg states, reveal the origin of this effect. The shelflike shape of the 1 (2)A(1) 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. (C) 2003 American Institute of Physics.