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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 IlB, I0B, C2H2, 13C2H2, and C2D2 reactions.Several structures of the HBC2 and BCzH2 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 BCzHz addition products) and three HBC2 species (linear HBCC, linear HCCB, and C2" HBC2). The BC2H2 borirene radical is photosensitive, forms spontaneously on annealing above 18 K, and exhibits calculated bond lengths appropriate for delocalized 7r 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 a b initio calculations.

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Reactions of pulsed laser produced B and N atoms at high dilution in argon favored diboron species. At low laser power with minimum radiation, the dominant reaction with N2 gave BBNN (3Π). At higher laser power, reactions of N atoms contributed the B2N (2B2), BNB (2Σu+), NNBN (1Σ+), and BNBN (3Π) species. These new transient molecules were identified from mixed isotopic patterns, isotopic shifts, and ab initio calculations of isotopic spectra.