Reactions of pulsed-laser evaporated boron atoms with hydrogen. Infrared spectra of boron hydride intermediate species in solid argon

Article abstract of DOI:10.1021/ja00090a048

Pulsed-laser ablated B atoms react with H₂ upon condensation with excess argon to give BH, a (H₂)(BH) complex, and B₂H₆ as the major products. The initial reaction to form BH requires activation energy, and BH reacts with H₂ to give additional products. Sharp new bands at 2587.3 and 1129.2 cm^-1 exhibit natural isotopic 1:4 doublets for vibrations involving a single boron atom and disappear on annealing to 25 K. Substitution of ¹⁰B and D gives shifts that are matched by MBPT(2) calculations of vibrational spectra for planar BH₃. Broader bands at 2475.2 and 1134.3 cm^-1 exhibit similar isotopic shifts for vibrations of a BH₃ submolecule and decrease on annealing to 25 K. The displacements from isolated BH₃ frequencies suggest a (H₂)(BH₃) complex and are in general agreement with recent quantum chemical calculations for BH₅. A sharp 2679.9-cm^-1 band gives the ¹⁰B shift predicted by MBPT(2) calculations for linear HBBH. A weak 2212.8-cm^-1 band exhibits the ¹⁰B shift and frequency calculated for the strongest band of BH₄^-. Additional broad absorptions that remain on annealing are attributed to higher boranes.