REVISED HEAT OF FORMATION FOR GASEOUS BORON - BASIS-SET LIMIT AB-INITIO BINDING-ENERGIES OF BF3 AND BF

To determine the heat of formation of boron atom, a fundamental parame ter in gas-phase thermochemistry, from a thermochemical cycle involvin g BS, the total atomization energy (TAE(0), Sigma D-0) of this molecul e was accurately determined ab initio in an exhaustive convergence stu dy using coupled cluster [CCSD(T)] methods. Basis sets up to [8s7p6d5f 4g3h2i] quality have been considered, and an extrapolation for further basis set incompleteness was applied. Inner-shell correlation, anharm onicity in the zero-point energy, and atomic spinorbit splitting have all been taken into account. Our best computed TAE(0) for BF3, 462.6 /- 0.3 kcal/mol, leads to a best heat of formation for gaseous boron a t 0 K of 136.0 +/- 0.4 kcal/mol, in excellent agreement with an experi mental determination of 136.2 +/- 0.2 kcal/mol and definitively confir ming recent suggestions that the established reference value, 132.7 +/ - 3.0 kcal/mol, should be revised. This revision will affect most know n gas-phase thermochemical data for boron compounds. As a byproduct, w e obtain a dissociation energy D-0 of 180.13 +/- 0.2 kcal/mol for the BF diatomic, in perfect agreement with experiment but with a much smal ler uncertainty.