MASS SPECTROMETRIC INVESTIGATION OF HIGH-TEMPERATURE REACTION OF HYDROGEN WITH BORON CARBIDE

The boron-containing gaseous molecules BH, BH3, HBC2, and BH2CxH2x+1 (x = 1 and 2) have been identified as products of a high-temperature reaction of hydrogen with boron carbide; higher molecular weight boron-carbon-hydrogen molecules may have been present, but they could not be observed because of interference from hydrocarbons formed in the reaction. Evidence for BH2 was not found. Concentrations of BH3 and the two alkylboranes far exceeded the predicted equilibrium quantities. This phenomenon is thought to result from a steady-state reaction in the crucible, and a mechanism is suggested. The other molecules, BH and HBC2, appeared to be present in near-equilibrium concentrations. Values for D°(BH-H) and D°(BH2-H) are discussed; revisions are suggested. Secondary electron multiplier gains determined for H, H2, and 11B are in the ratio 1:3.5:19.2 for 6.5-kV ions. D (H-BC2) is determined to be 100 ± 10 kcal/mol.