Isomerization Mechanisms of C_5H_2 on the Triplet and Singlet Potential Energy Surfaces

Density functional theory calculations with the B3LYP functional are used to study the structure and stabilities of C₅H₂ isomers and possible isomerization mechanisms on the triplet and singlet potential energy surfaces. Calculated results show that isomerization of C₅H₂ is likely to occur on the triplet potential energy surface while direct conversions of the singlet C₅H₂ isomers via 1,3‐hydrogen migration transition states are extremely difficult dynamically. In such isomerization processes, the hydrogen transfer processes in carbon chains are the rate‐determining steps. The triplet species except the linear ground state X³ Σ are rather less stable than their singlet forms, although the singlet and triplet species have similar geometries.