Valence space electron momentum spectroscopy of diborane

A non-classical mechanism of binding in diborane (B2H6) is derived quantum-mechanically (B3LYP/6-31 1++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, 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-h, (b) all bonds in diborane are electron-deficient including the four equivalent B-H, bonds, (c) there is no pure B-B bond but contributions front all valence orbitals form an unconventional electron-deficient B-B bond, and (d) only two innermost valence orbitals - 2a(g) and 2b(lu)- are sp(2)-hybridized and no evidence indicates other valence orbitals of diborane to be hybridized. (c) 2006 Elsevier B.V. All rights reserved.