Formic acid-methanol complexation esterification: elusive pre-reactive species identified by vibrational spectroscopy.

Vibrational spectra of the mixed dimer and the two mixed trimers of methanol and formic acid as well as some of their isotopologues are presented. Out of the eight expected OH stretching fundamentals of these three pre-reactive hydrogen-bonded complexes, the three modes mainly involving an acid OH group bound to the alcohol appear to be missing in the jet-cooled spectra despite a combination of infrared and Raman probing. A possibility of spectral overlap is discussed in the mixed dimer case, but largely discarded.

Quantifying Conformational Isomerism in Chain Molecules by Linear Raman Spectroscopy: The Case of Methyl Esters.

The conformational preferences of the ester group have the potential to facilitate the large amplitude folding of long alkyl chains in the gas phase. They are monitored by Raman spectroscopy in supersonic jet expansions for the model system methyl butanoate, after establishing a quantitative relationship with quantum-chemical predictions for methyl methanoate. This requires a careful analysis of experimental details, and a simulation of the rovibrational contours for near-symmetric top molecules.

2-Methoxyethanol: harmonic tricks, anharmonic challenges and chirality-sensitive chain aggregation.

The Raman spectrum of jet-cooled, nearly monoconformational 2-methoxyethanol reveals a strong, aggregation-sensitive resonance in the backbone stretching region and pronounced chirality-dependent dimerisation effects in the OH stretching region. These effects are disentangled by a dual-detection scheme which simultaneously probes the two spectral regions. The performance of mass-scaled harmonic wavenumber predictions and of vibrational perturbation theory in reproducing these spectral features is explored.

The Chiral Trimer and a Metastable Chiral Dimer of Achiral Hexafluoroisopropanol: A Multi-Messenger Study.

1,1,1,3,3,3-hexafluoro-propan-2-ol aggregates preferentially into an achiral dimer of achiral monomers, but the trimer is found to prefer three metastable chiral monomer units arranged into a strained OH⋅⋅⋅O hydrogen-bonded ring, which is reinforced by secondary CH⋅⋅⋅FC interactions. This is shown by a combination of infrared, microwave, and Raman spectroscopy in supersonic jet expansions and supported by high-level quantum chemical calculations. It involves an activation of the monomers by >15 kJ mol , clearly driven by the much stronger hydrogen-bond interaction available to the gauche and even more to the cis monomer units.

Matrix-Isolation and Quantum-Chemical Analysis of the C Conformer of XeF, XeOF, and Their Acetonitrile Adducts.

A joint experimental-computational study of the molecular structure and vibrational spectra of the XeF molecule is reported. The vibrational frequencies, intensities, and in particular the isotopic frequency shifts of the vibrational spectra for XeF and XeF isotopologues recorded in the neon matrix agree very well with those obtained from relativistic coupled-cluster calculations for XeF in the C structure, thereby strongly supporting the observation of the C conformer of the XeF molecule in the neon matrix. A C transition state connecting the C and O local minima is located computationally.