Abstract: Ab initio calculations for B₂H₅⁺ cation, neutral B₂H₅^· radical and B₂H₅^- anion has been performed at the B3LYP/6311G (d, p) level and further the single point calculations are carried out at QCISD(T)/6311++G (3df, 2p) level. Two isomers for B₂H₅⁺ cation are found with triply bridged D_3h and singly bridged C₁ while the former is more stable in energy. Two new isomers (C₁, C₁) for the triplet excited state are optimized with asymmetric doubly bridged bond. Also four isomers including two new symmetries with doubly and triply bridged C_s and C_s are predicated for B₂H₅^· radical. In all cases the single hydrogen bridge isomer is found to be more stable than others. We also optimize the C_2v symmetries using different methods and levels. It is shown that all results have one imaginary frequency and thus it does not correspond to a local minimum on the potential surface but perhaps to a saddle point. In the end, we support two isomers for B₂H₅^- anion with singly bridged C_2v and doubly bridged C_s, while for triplet excited state of B₂H₅^- anion only C_2v with single bridge would be stable, though they have not been successfully isolated now.

Key words: Quantum chemical calculation, Triplet excited state, Potential energy surface, Three center with two electron hydrogen bridge bond