Observation and Characterization of the Hg-O Diatomic Molecule: A Matrix-Isolation and Quantum-Chemical Investigation

Mercuric oxide is a well-known and stable solid, but the diatomic molecule Hg-O is very fragile and does not survive detection in the gas phase. However, laser ablation of Hg atoms from a dental amalgam alloy target into argon or neon containing about 0.3 % of ¹⁶ O₂ or of ¹⁸ O₂ during their condensation into a cryogenic matrix at 4 K allows the formation of O atoms which react on annealing to make ozone and new IR absorptions in solid argon at 521.2 cm^-1 for Hg-¹⁶ O or at 496.4 cm^-1 for Hg-¹⁸ O with the oxygen isotopic frequency ratio 521.2/496.4=1.0499. Solid neon gives a 529.0 cm^-1 absorption with a small 7.8 cm^-1 blue shift. CCSD(T) calculations found 594 cm^-1 for Hg¹⁶ O and 562 cm^-1 for Hg¹⁸ O (frequency ratio=1.0569). Such calculations usually produce harmonic frequencies that are slightly higher than the anharmonic (observed) values, which supports their relationship. These observed frequencies have the isotopic shift predicted for Hg-O and are within the range of recent high-level frequency calculations for the Hg-O molecule. Spectra for the related mercury superoxide and ozonide species are also considered for the first time.