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)O(2) or of (18)O(2) 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 Hg(16)O and 562 cm(−1) for Hg(18)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.