On the structure and normal modes of hydrogenated Ti-fullerene compounds

When titanium covers a C₆₀ core, the metal atoms may suppress the fullerene's capacity of storing hydrogen, depending on the number of Ti atoms covering the C₆₀ framework, the Ti–C binding energy, and diffusion barriers. In this article, we study the structural and vibrational properties of the C₆₀TiH _n (n = 2, 4, 6, and 8) and C₆₀Ti₆H₄₈ compounds. The IR spectra of C₆₀TiH _n compounds have a maximum attributable to the Ti–H stretching mode, which shifts to lower values in the structures with n = 4, 8, while their Raman spectra show two peaks corresponding to the stretching modes of H₂ molecules at apical and azimuthal positions. On the other hand, the IR spectrum of C₆₀Ti₆H₄₈ shows an intense peak due to the Ti–H in-phase stretching mode, while its Raman spectrum has a maximum attributed to the pentagonal pinch of the C₆₀ core. Finally, we have found that the presence of one apical H₂ molecule enhances the pentagonal pinch mode, becoming the maximum in the Raman spectrum.