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 f FBO and BO + O f BO 2 . It is shown that ∆H (298 K) and ∆H (2000 K) differ, on the average, by only 1.5 kcal/mol; however, ∆G 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.

A Crossed Molecular Beam Study on the Reaction of Boron Atoms with Methylacetylene and Partially Deuterated Methylacetylene

“…Due to its high energy density, both in volume and gravity terms, [1,2] boron has long been regarded as a good candidate for rocket fuel additives. [3][4][5][6] To fulfill this potential, it is essential to understand the boron combustion chemistry and the reactions of boron atoms with hydrocarbon fuels on the molecular level.…”

“…Therefore, elementary reactions of ground-state boron atoms, BA C H T U N G T R E N N U N G ( 2 P j ), with unsaturated hydrocarbons and the thermodynamical properties of boron-substituted hydrocarbons have been investigated both experimentally and theoretically. Before experimental data became available, theoreticians had predicted that the cyclic, 2p-Hückel aromatic compound borirene, (CH) 2 BH, is thermodynamically stable [ Figure 1, (1)]. [7][8][9][10] Efforts have also been made to understand the effect of boronsubstitution and insertion reactions into hydrocarbon molecules.…”

“…Utilizing the CD 3 CCH reactant, detailed information on the dynamics is obtained. The reaction followed indirect scattering dynamics and proceeded through at least two reaction channels via atomic deuterium and hydrogen atom elimination pathways leading eventually to two isotopomers, that is, the C 2v symmetric D 2 atomic hydrogen exchange channel is open. The reaction dynamics were suggested to be indirect, proceeded via addition of the boron atom to the carbon-carbon triple bond via a cyclic intermediate, and formed-after successive isomerizations and a hydrogen elimination-the linear Figure 1, (2)].…”

Computational prediction of standard gas, liquid, and solid‐phase heats of formation and heats of vaporization and sublimation

“…An alternative approach is to compute Δ H ° for the atomization of the molecule (i.e., dissociation into its constituent atoms) and to combine this appropriately with the experimental enthalpies required to produce these atoms from the respective stable elements. These procedures can be quite accurate for molecules small enough that high‐level computational methods can be used; with the ab initio CBS‐QB3 technique, for example, we obtained gas‐phase Δ H for a series of boron and aluminum combustion products with an average absolute deviation from experiment of <2.0 kcal/mol 6–8. Other studies have yielded G3 heats of formation 9 and CBS‐QB3 atomization enthalpies 10 that are accurate, on average, to within 1.0 kcal/mol.…”

Theoretical Prediction of Heats of Sublimation of Energetic Materials Using Pseudo‐Atomic Orbital Density Functional Theory Calculations

“…For instance, Politzer proposed approaches based on macroscopic condensed phase properties, which depend upon non-covalent interactions and can be expressed analytically, with good accuracy, in terms of a small subset of a group of statistically defined quantities that characterize molecular surface electrostatic potentials [1 -5]. These approaches have been successfully applied using quantum chemistry calculations, such as hybrid density functional theory (DFT) [3,4], and correlation methods for instance the coupled cluster singles, doubles and triples (CCSDT) method which gives very accurate correlation energies but as it is well known these calculations are computationally very demanding [6]. It is also known that these high-level quantum chemistry methods are usually limited to small molecules and clusters with small basis sets.…”