Theoretical study of B2H+4 and B2H4

An ab initio molecular orbital study is presented of B2H+4 and B2H4 at the G1 level of theory, including correlation energy beyond fourth-order perturbation theory and large basis sets. The B2H+4 ion is predicted to have a nonplanar doubly hydrogen-bridged C2v structure [HB(H2)H]. For B2H4, two structures of nearly equal energy are found, confirming previous work by Mohr and Lipscomb. One is a nonplanar doubly hydrogen-bridged structure similar to the cation and the other is a D2d H2BBH2 structure. The theoretical results suggest that the recently measured appearance potential for B2H6→B2H+4+H2+e does not correspond to the lowest energy form of B2H+4, but rather to a triply bridged isomer closely related to the most stable form of B2H+5.