Valence space electron momentum spectroscopy of diborane

Abstract

A non-classical mechanism of binding in diborane (B 2 H 6) is derived quantum-mechanically (B3LYP/6-311++G**) using a dual-space analysis. High-resolution binding-energy spectra of diborane, generated using an outer-valence Green’s-function and density-functional theory with a statistical average of model orbital potentials (SAOP), agree satisfactorily with experiment. Electron-correlation energies of diborane produce orbital-based variations in ionization energy in the valence space, but with negligible impact on the shape of only a g symmetry orbitals as indicated in momentum space. The present work indicates quantitatively that (a) the pair of three-centre banana-shaped B H b B bonds are more accurately described as one diamond-shaped bond with B H b B H b , (b) all bonds in diborane are electron-deficient including the four equivalent B H t bonds, (c) there is no pure B B bond but contributions from all valence orbitals form an unconventional electron-deficient B B bond, and (d) only two innermost valence orbitals – 2a g and 2b 1u – are sp 2-hybridized and no evidence indicates other valence orbitals of diborane to be hybridized.