A hydrogen-bonded CHFaHF 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.