The effect of hydrogen bonding on torsional dynamics: A combined far-infrared jet and matrix isolation study of methanol dimer.

The effect of strong intermolecular hydrogen bonding on torsional degrees of freedom is investigated by far-infrared absorption spectroscopy for different methanol dimer isotopologues isolated in supersonic jet expansions or embedded in inert neon matrices at low temperatures. For the vacuum-isolated and Ne-embedded methanol dimer, the hydrogen bond OH librational mode of the donor subunit is finally observed at ∼560 cm(-1), blue-shifted by more than 300 cm(-1) relative to the OH torsional fundamental of the free methanol monomer. The OH torsional mode of the acceptor embedded in neon is observed at ∼286 cm(-1). The experimental findings are held against harmonic predictions from local coupled-cluster methods with single and double excitations and a perturbative treatment of triple excitations [LCCSD(T)] and anharmonic. VPT2 corrections at canonical MP2 and density functional theory (DFT) levels in order to quantify the contribution of vibrational anharmonicity for this important class of intermolecular hydrogen bond vibrational motion

High-resolution rovibrational analysis of CH281BrF in the range 920-980 cm-1

The high-resolution infrared spectrum of CH281BrF has been studied in part of the atmospheric window between 920 and 980 cm-1, the region characterized by the ν9 and v5+v6 absorptions. The v9 emerges as a pseudo a-type band, with selection rule DKa = DKc = 0, +/-2, and v5+v6 exhibits a predominant a-type structure. The interactions connecting these levels and the dark 3v6 state have been explored. The anomalous v9 transitions have been ascribed to Coriolis interaction with v4. The analysis yields a set of accurate upper-state parameters for v9 and v5+v6. Spectroscopic information on 3v6 has been also obtained