The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF2Cl2 molecule and a cyclic water trimer (H2O)3 were used as halocarbon and water cluster, respectively. The dynamics calculation of CF2Cl2 showed that both C–Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF2Cl as a Cl? ion. Almost all total available energy was transferred into the internal modes of the parent CF2Cl radical on the product state, while the relative translational energy of Cl? was significantly low due to the elongation of two C–Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF2Cl2(H2O)3 showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other Cl atom existed as a dangling Cl atom. After the electron capture, only one C–Cl bond (dangling Cl atom) was rapidly elongated, whereas the other C–Cl bond is silent during the reaction. The dangling Cl atom was directly dissociated from CF2Cl(H2O)3 as Cl?. The fast Cl? ion was generated from CF2Cl(H2O)3 on the water cluster. The mechanism of the electron capture of halocarbon on water ice was discussed on the basis of the theoretical results. ©2007 American Institute of Physics