The conformers of oxalyl chloride [(ClCO)_2] have been extensively studied both theoretically and experimentally while the structure of its cation [(C1CO)2+ ] has received less attention. On the other hand, the theoretical study on the single molecule dissociation of oxalyl chloride cation is a whole new aspect. In the present work, the conformers of oxalyl chloride cation was studied at the BHandHLYP level with 6-311 + G(d) and 6-311 + G(2df) basis sets. It is found that (C1CO)_2+ have gauche and trans conformeis. The orbital interactions in the gauche conformer make it possible to stabilize itself. The C-C bonds in both of the conformers are longer than that in the oxalyl chloride neutral molecule, which suggests in advance that C-C bond in (C1CO)2+ can have some different properties from that in (C1CO)_2. According to the reaction Gibbs free energy calculated at the BHandHLYP/6-311 + G(2df) level, the dissociation of C-C bond in (C1CO)2+ is easier than that in (C1CO)2- The reaction mechanism confirms this thermodynamic conclusion which is in accord with the experimental results. The frequencies of all the vibrant modes in (C1CO)2+ and the coupling constants between the C-C bond vibrancy and other vibrant modes are also studied. The results indicate that (C1CO) 2+ bears bond selectivity in C-C bond dissociation. It suggests that it is possible to excite the vibrancy of C-C bond to a high level with selected laser light, and so that C-C bond can break down at this level.

Key words: DFT, ACYL CHLORIDES, THERMODYNAMICS, CONFORMATION