PULSED-LASER EVAPORATED BORON ATOM REACTIONS WITH ACETYLENE - INFRARED-SPECTRA AND QUANTUM-CHEMICAL STRUCTURE AND FREQUENCY CALCULATIONS FOR SEVERAL NOVEL BC2H2 AND HBC2 MOLECULES

Pulsed laser evaporated boron atoms react with C2H2 to form new organoborane products during condensation with excess argon. Isotopic frequencies have been obtained for the B-11, B-10, C2H2, (C2H2)-C-13, and C2D2 reactions. Several structures of the HBC2 and BC2H2 molecules have been studied ab initio using large basis sets and augmented coupled cluster methods. Computed isotopic shifts are in excellent agreement with experiment for two BC2H2 SpeCies (bent HBCCH insertion and ring BC2H2 addition products) and three HBC2 Species (linear HBCC, linear HCCB, and C2v HBC2). The BC2H2 borirene radical is photosensitive, forms spontaneously on annealing above 18 K, and exhibits calculated bond lengths appropriate for delocalized pi bonding in the BC2 ring system. The linear HBCC and HCCB species are formed by the reaction of hyperthermal B atoms and C2H2 during matrix deposition. Thermochemistry has been addressed by ab initio calculations.