The B3Li molecule’s electronic and geometrical structure

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Abstract
The geometries, electronic energies, dipole moments, and local harmonic vibrational frequencies of the singlet ground and low‐energy singlet valence excited states of B3Li have been investigated using (i) correlation‐consistent double‐zeta plus polarization basis sets, (ii) small valence‐space complete active space multiconfiguration self‐consistent field electronic wave functions, and (iii) analytical energy derivative techniques combined with automated potential energy surface ‘‘walking’’ algorithms. The lowest‐energy structure of B3Li is found to have C3v symmetry and to consist of a Li atom that sits above the center of an equilateral B3 moiety; the dipole moment of this species is 6.7 D and its dissociation energy (not zero point corrected) to ground state B3+Li is 60 kcal/mol. The B3H analog of this C3v structure is not a geometrically stable species for reasons that are analyzed here. A second stable structure (with dipole moment of 8.5 D and dissociation energy of 47 kcal/mol) is planar and has the Li atom σ bonded to one of the B atoms in the triangular B3 group. The B3H analog of this σ‐bonded species is stable and, in fact, is the lowest‐energy structure of B3H. Finally, in contrast to findings for B3H, no bridge‐bonded structure was found to be stable for B3Li. Both the σ‐bonded and C3v structures of B3Li are shown to possess significant charge–transfer character near their equilibrium geometries, but to dissociate to ground state neutral B3+Li fragments.