THE COMBINED INELASTIC NEUTRON SCATTERING (INS) AND SOLID-STATE DFT STUDY OF HYDROGEN-ATOMS DYNAMICS IN KAOLINITE-DIMETHYLSULFOXIDE INTERCALATE

Vibrational spectra of two kaolinite-dimethylsulfoxide intercalates, obtained using inelastic neutron scattering (INS), were analyzed with a view to understanding the dynamics of the hydrogen atoms in the structure. The main focus was on the spectral region 0-1700 cm(-1), which is difficult to analyze using optical spectroscopy. The experimental vibrational spectra of kaolinite:dimethylsulfoxide and kaolinite:d6-dimethylsulfoxide collected using two different spectrometers were interpreted by means of the solid-state DFT calculations. Calculated spectra were obtained by both normal-mode analysis and molecular dynamics going beyond the harmonic approximation. The Al-O-H bending modes were found to be spread over the large interval 100-1200 cm(-1), with the dominant contributions located between 800 and 1200 cm(-1). The shape of the individual hydrogen spectrum depends on whether or not the respective hydrogen atom is involved in an O-H center dot center dot center dot O hydrogen bond and on its strength. The modes corresponding to the in-plane movements of the inner-surface hydrogen atoms are well defined and always appear at the top of the intervals of energy transfer. In contrast, the modes generated by the out-of-plane movements of the hydrogen atoms are spread over large energy intervals extending down to the region of external (lattice) modes. The C-H modes are concentrated mainly in the three regions 1200-1450 cm(-1), 800-1100 cm(-1), and 0-400 cm(-1). While the first two regions are typical of the various deformational modes of methyl groups, the low-energy region is populated by the modes corresponding to the movements of the whole dimethylsulfoxide molecule.