ESR of the BO Molecule in Inert Matrices: A Case of Extreme Preferential Orientation

The BO molecule has been trapped in neon and argon matrices at 4°K in its ground 2Σ state and investigated by ESR spectroscopy. It is trapped in only one site in solid neon and is highly oriented with respect to the sapphire surface of condensation. The neon spectra indicate that BO molecules lie in vertical planes perpendicular to the surface and an analysis of their distribution within the planes places them preferentially either perpendicular or parallel to the surface. The derived magnetic parameters in neon are g‖ = 2.0012(3), g⊥ = 2.0015(3), A‖(11B) = 1018(1) MHz, A⊥(11B) = 1034(1) MHz. A‖ < A⊥ implies that the dipolar nuclear hf coupling is negative, a unique condition in diatomics. It is shown that it may be accounted for by including the effects of AO's centered on oxygen in the dipolar interaction at the boron nucleus.