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 16O2 or of 18O2 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‐16O or at 496.4 cm−1 for Hg‐18O 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 Hg16O and 562 cm−1 for Hg18O (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. Mercury atoms from laser ablation of a dental amalgam target react with oxygen atoms upon co‐condensation in excess argon and neon, and they provide frequencies of 521.2 and 529.0 cm−1, respectively, which support high‐level calculations for this weakly bound Hg−O diatomic molecule. The small difference between our neon and argon matrix observations for Hg−O suggest a slightly ionic molecule. Spectra are also observed for Hg‐O2 and Hg‐O3.