FIRST GAS PHASE DETECTION OF THE CLOSED SHELL BORON SPECIES HBCC(X 1 Sigma) - A CROSSED BEAM STUDY OF B( 2 P) WITH C 2 H 2 ( 1 Sigma g + )

novel supersonic beam of ground-state boron atoms [B(2P)] was employed to investigate the reaction of B(2P) with acetylene [C2H2(1Σg+)] 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 (11BC2H+), 35 (10BC2H+/11BC2+), and 34 (10BC2+) at different laboratory angles. Forward-convolution fitting of the laboratory data showed that only a product with the gross formula BC2H 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(2P) to the two carbon atoms of acetylene, leading to the formation of a first intermediate, the borirene radical (c-BC2H2). This intermediate underwent various isomerization processes on the BC2H2 potential energy surface before decomposing into the linear HBCC(X1Σ) isomer via a hydrogen atom elimination.