Characterization of α-hydroquinone and β-hydroquinone clathrates by THz time-domain spectroscopy

We have measured the absorption spectra of α-hydroquinone and methane- and methanol-loaded β-hydroquinone clathrates up to 3 THz frequency range using terahertz time-domain spectroscopy (THz-TDS). The α-hydroquinone exhibits 11 resonances whereas methane- and methanol-loaded β-hydroquinone clathrates show only 1 resonance. The observed THz resonances represent the intermolecular and lattice vibrations of the hydroquinone frameworks, but seem to be insensitive to the encaged guest species. The indices of refraction are found to be ca. 1.6 for α-hydroquinone and methane-loaded β-hydroquinone clathrate and 1.7 for methanol-loaded β-hydroquinone clathrate, and the anomalous dispersions are well-defined at the resonance frequencies.