Density functional theory (B3LYP) along with 6-31G** and 6-31＋＋G** basis sets was employed to investigate the photodissociation reactions of thiophene. According to the experiment results, five photolysis channels have been examined, including three closed-shell molecular channels yielding C₄H₄＋S, C₂H₂＋C₂H₂S, and CS＋C₃H₄, and two radical channels yielding HCS＋C₃H₃ and HS＋C₄H₃. The most probable isomers of the product fragments were determined. It was found that the reaction yielding C₄H₄＋S was the most energetically favorable in the triplet state and c-C₄H₄S→C₂H₂＋C₂H₂S was preferential in the ground state. The calculation results show that C₂H₂＋C₂H₂S, which were found to be the major products, were formed mainly in the ground state. By comparison of the computational results with the experimental findings, it can be concluded that the photodissociation mechanism of thiophene is dependent on the wave length.

Key words: thiophene, photodissociation, reaction mechanism, B3LYP