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 organo borane products during condensation with excess argon. Isotopic freque ncies have been obtained for the B-11, B-10, C2H2, (C2H2)-C-13, and C2 D2 reactions. Several structures of the HBC2 and BC2H2 molecules have been studied ab initio using large basis sets and augmented coupled cl uster methods. Computed isotopic shifts are in excellent agreement wit h experiment for two BC2H2 SpeCies (bent HBCCH insertion and ring BC2H 2 addition products) and three HBC2 Species (linear HBCC, linear HCCB, and C2v HBC2). The BC2H2 borirene radical is photosensitive, forms sp ontaneously on annealing above 18 K, and exhibits calculated bond leng ths appropriate for delocalized pi bonding in the BC2 ring system. The linear HBCC and HCCB species are formed by the reaction of hypertherm al B atoms and C2H2 during matrix deposition. Thermochemistry has been addressed by ab initio calculations.