Accurate binding energies of diborane, borane carbonyl, and borazane determined by many-body perturbation theory

Binding energies including valence-shell electron correlation are obtained from many-body perturbation theory (MBPT) for diborane, borane carbonyl, and borazane. Results are given for basis sets of double zeta quality and for basis sets with polarization functions added on all atoms. The binding energies (-..delta..E) are found to be (respectively) 35, 21, and 30 kcal/mol. Correlation effects account for 48, 62, and 32% of the binding. The size-consistent nature of the MBPT method enables the computation of enthalpies of reaction for four different reactions involving monoborane, diborane, carbon monoxide, and borane carbonyl. When the theoretical values are corrected for vibrational zero-point energies and the experimental data are adjusted for temperature effects, the results agree (within 5%) and thus confirm the set of experimental enthalpies corresponding to ..delta..H (300/sup 0/C) = -34 kcal/mol for the association reaction yielding diborane. The result for the binding energy of borazane constitutes a prediction in the absence of an experimental value.