PNNL

Abstract

Atomization energies at 0 K and heats of formation at 0 K and 298 K are predicted for (CH3)H2N-BH3, (CH3)HN=BH2, (BH3)HN=CH2, (CH3)H2B-NH3, (CH3)HB=NH2, and (NH3)HB=CH2, as well as various molecules involved in the different bond breaking processes, from coupled cluster theory (CCSD(T)) calculations. In order to achieve near chemical accuracy (±1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen core CCSD(T) energies: corrections for core-valence, scalar relativistic, and first order atomic spin-orbit effects. Scaled vibrational zero point energies were computed with the MP2 method. The heats of formation were predicted for the respective dimethyl- and trimethyl- substituted ammonia boranes, their dehydrogenated derivatives, and the various molecules involved in the different bond breaking processes, based on isodesmic reaction schemes calculated at the G3(MP2) level. Thermodynamics for dehydrogenation pathways in the monomethyl substituted molecules were predicted. Dehydrogenation across the B-N bond is more favorable as opposed to dehydrogenation across the B-C and N-C bonds. Methylation at N reduces the exothermocity of the dehydrogenation reaction and makes the reaction more thermoneutral while methylation at B moves it away from thermoneutral. This work was supported by the US Department of Energy Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.