The photodissociation of dichloromethane (CH2Cl2) has been investigated by spin-orbit ab initio calculations. The potential energy curves were calculated by multi-state second order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction (MS-CASPT2/CASS1-SO). The calculated results clearly assigned the experimentally observed photodissociation channels from the first and second singlet excited states leading to CH2Cl. + Cl(P-2(3/2)) and CH2Cl.(+) Cl*((2)p(1/2)). The reason of higher Cl*/Cl ratios in vibrationally mediated photodissociation than in vibrationless one was discussed. (c) 2007 Elsevier B.V. All rights reserved.