B atoms, B2 and H2BO molecules: ESR and optical spectra at 4 °K

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Abstract
Elemental boron has been vaporized and trapped in solid argon at 4–10 °K. The Douglas–Herzberg transition of B2 has been observed in absorption at 3300 Å at 10 °K, indicating that the lower Σ state is the ground electronic state. However, B2 was not observed via ESR, which is interpreted as support for a 3Σ−g ground state with a zero-field splitting greater than about 4 cm−1, rather than 5Σ−u favored by ab initio calculations. The ESP spectrum of B atoms in solid argon is also detected. It exhibits axial symmetry and almost complete quenching of the orbital angular momentum of the 2P1/2 free atom, with g∥=2.0014(5), g⊥=1.9645(30). The simple crystal field model has been applied in the interpretation of the g and hyperfine tensors and comparison made with Al and Ga in argon, as studied by Ammeter and Schlosnagle. The ESR spectrum of H2BO, appearing as an impurity, was observed for the first time, and its magnetic parameters determined.