Theoretical study of the ionization of B2H5

Ab initio molecular orbital calculations at the G1 level of theory have been carried out on neutral B2H5 radical, doubly bridged B2H+5 cation, and the first triplet excited state of B2H+5. Singly bridged B2H5 is 4.0 kcal/mol (without zero-point energies) more stable than doubly bridged B2H5. Based on this work and previous theoretical work on triply bridged B2H+5, ionization potentials (vertical and adiabatic) are determined for B2H5. The adiabatic ionization potentials of the two B2H5 structures are 6.94 eV (singly bridged) and 7.53 eV (doubly bridged). A very large difference is found between the vertical and adiabatic ionization potentials (3.37 eV) of the singly bridged B2H5 structure. The first triplet state of B2H+5 is found to be 4.55 eV higher in energy than the lowest energy B2H+5 cation (triply bridged). The results of this theoretical study support the interpretation of Ruscic, Schwarz, and Berkowitz of their recent photoionization measurements on B2H5