Photochemistry of the H2O/CO System Revisited: The HXeOH···CO Complex in a Xenon Matrix

A hydrogen-bonded CHF⋯HF complex: IR spectra and unusual photochemistry

A hydrogen-bonded CHF⋯HF complex was characterized by FTIR matrix isolation spectroscopy and ab initio calculations. Three possible structures of this complex were found at the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)/L3a_3] level of theory. The comparison between the experiment and theory reveals that the most stable structure with the binding energy of 6.48 kcal/mol is formed upon x-ray irradiation of isolated CH₂F₂ molecules in noble gas matrices (Ne, Ar, Xe). This species appears to be the first known intermolecular complex of monofluorocarbene, and its identification was unambiguously proved by IR absorptions corresponding to HF deformation (libration), CF stretching, H-C-F bending, and CH and HF stretching modes. It is worth noting that the corresponding spectral features in an argon matrix were previously tentatively ascribed to CH₂F₂ ^+· and HF⋯CHF^-· [L. Andrews and F. T. Prochaska, J. Chem. Phys. 70, 4714 (1979)], but the calculations performed in the present study definitely support the re-assignment. The observed CHF⋯HF complex can be converted to the parent CH₂F₂ under the action of light with λ < 525 nm. The plausible mechanism of this conversion using the conical intersection concept is discussed.

Computational Structures and SAPT Interaction Energies of HXeSH···H2Y (Y=O or S) Complexes

Ab initio calculations of the structures, vibrational spectra and supermolecular and symmetry-adapted perturbation theory (SAPT) interaction energies of the HXeOH and HXeSH complexes with H2O and H2S molecules are presented. Two minima already reported in the literature were reproduced and ten new ones were found together with some transition states. All complexes show blue shift in Xe–H stretching mode upon complexation. The computed spectra suggest that it should be possible to detect and distinguish the complexes experimentally. The structures where H2O or H2S is the proton-donor were found to be the most stable for all complex compositions. The SAPT analysis shows significant differences between the complexes with H2O and H2S indicating much larger dispersion and exchange contributions in the complexes with H2S.