Abstract
The interaction of difluoromethane (CH 2F 2) with the TiO 2 surface (P25 Degussa) at room temperature has been studied by Fourier-transform infrared spectroscopy for the first time. From the comparison between the adsorption characteristics and the gas-phase spectra it can be deduced that the molecule adsorbs through an acid–base interaction between one F atom and the surface Lewis acid site (Ti 4+) and an H-bond between the CH 2 group and the surface Lewis basic site (OH − or O 2−). In order to obtain more information about the orientation geometry and the variation of the molecular structural parameters, a quantum-mechanical investigation at DFT/B3LYP level has been also performed, considering the anatase (1 0 1) surface and focusing on the O 2− as Lewis basic site. The resulting adsorbate–substrate structures involve the formation of an acid–base interaction between one F atom and the Ti 4+ ion and differ for the number of the involved H-bonds. According to the scaled vibrational frequencies, the simulated adsorption model which better agrees with the experimental data corresponds to that in which the CH 2 group interacts with the surface by only one H-bond.
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