Gas‐phase detection of the HBCC (X 1 Σ) molecule: a combined crossed beam and computational study of the B( 2 P)+C 2 H 2 ( 1 Σ g + ) reaction

A novel supersonic beam of ground‐state boron atoms [B( 2 P)] was employed to investigate the reaction of B( 2 P) with acetylene [C 2 H 2 ( 1 Σ g + )] at an average collision energy of 16.3±0.4 kJ mol −1 at the most fundamental microscopic level. The crossed molecular beam technique was used to record time of flight spectra at mass to charge ratios of 36 ( 11 BC 2 H + ), 35 ( 10 BC 2 H + / 11 BC 2 + ), and 34 ( 10 BC 2 + ) at different laboratory angles. Forward‐convolution fitting of the laboratory data showed that only a product with the gross formula BC 2 H was formed via a boron versus hydrogen exchange. By combining experimental results with electronic structure calculations, the conclusion was that the reaction proceeded via the initial addition of B( 2 P) to the two carbon atoms of acetylene, leading to the formation of a first intermediate, the borirene radical (c‐BC 2 H 2 ). This intermediate underwent various isomerization processes on the BC 2 H 2 potential energy surface before decomposing into the linear HBCC(X 1 Σ) isomer via a hydrogen atom elimination. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1359–1365, 2001