Molecular Energetics of Borane Carbonyl and the Symmetric Dissociation Energy of Diborane

Large concentrations of borane, BH3, are produced upon the pyrolysis of borane carbonyl. Ionization efficiency measurements using a fast inlet mass-spectrometric technique, have led to I(BH3) as well as A(B+), A(BH+), A(BH2+), and A(BH3+) from BH3CO. These numbers permit a complete development of the molecular energetics of BH3CO and a confirmation of the symmetric dissociation energy of diborane of 59 kcal/mole. Earlier equilibrium data on the BH3CO decomposition, combined with these electron-impact data, also confirm D(BH3–BH3) = 59 kcal/mole. Earlier kinetic studies that suggest a very much lower dissociation energy are shown to be equivocal at best.