Computational Determination of the Energetics of Boron Ignition/Combustion Reactions

Abstract

Two computational procedures, the density functional B3PW91/6-311+G(2df,2pd) and the ab initio CBS-Q, have been used to calculate optimized geometries, energy minima at 0 K and enthalpies and free energies at 298 K for atoms and molecules involved in the ignition and/or combustion of boron. Calculated gas-phase heats of formation are presented for 58 atoms and molecules and are used to find heats of reaction for 83 possible ignition/combustion steps. The most exothermic are found to be BO + F → FBO and BO + O → BO2. It is shown that ΔH (298 K) and ΔH (2000 K) differ, on the average, by only 1.5 kcal/mol; however, ΔG can change quite considerably over the same temperature range. Relative stabilities and equilibrium constants are given for five pairs of isomers. While the geometries were obtained more accurately by the B3PW91 procedure, the CBS-Q is more reliable for heats of formation and heats of reaction.