Excited states and photodissociation processes of X+-pyridine complexes (X = Be, Mg, Ca) have been investigated by the time-dependent density functional approach. Calculations show that the cation-molecule complexation significantly modifies the properties of relevant excited states in complexes. Photodissociation of the Mg+-pyridine includes three channels: direct non-reactive predissociation, direct charge transfer (CT) dissociation, and predissociative CT reaction. The non-reactive dissociation is induced by the strong s --> p excitation from Mg+ moiety, and followed by the internal conversion from the excited state to the ground state through E - V quenching. Direct and predissociative CT processes arise from decay of CT and non-CT excited states. (C) 2004 Published by Elsevier B.V.