A DIMERIZATION REACTION INDUCED BY HYDROGEN-ATOMS - FROM B(CH3)(3) ADSORBED ON C PT(100) TO B2H2(CH3)(4)/

Monolayers of trimethylborane, B(CH3)(3), were prepared on graphite-mo nolayer-covered Pt(100) surfaces. The interaction of gaseous hydrogen atoms with these monolayers was investigated by thermal desorption and high-resolution electron energy-loss spectroscopies. At 80 K substrat e temperature, tetramethyldiborane, B2H2(CH3)(4), was observed as an a dsorbed reaction product. The reaction cross-section of 0.4 Angstrom(2 ) is compatible with a direct, Eley-Rideal type reaction mechanism. Fr om similar experiments with deuterium atoms it is apparent that H/D ex change at the methyl groups through a sequence of abstraction and addi tion also occurs, although with a smaller cross-section. The reaction pathway to tetramethyldiborane involves dimerization of a BH(CH3)(2) i ntermediate. Three possibilities for the reaction pathway to this inte rmediate are discussed. (C) 1995 Elsevier Science B.V. All rights rese rved.