Far-infrared and THz absorption spectra were obtained for thymine bases. Quantum chemical calculations were also conducted to simulate the far-infrared spectrum using density functional theory. Three models were used for the simulations. In one model, a thymine monomer was assumed. The second model assumed a thymine dimer, where two pyrimidine rings were aligned antiparallel. The last model assumed a thymine trimer, in which four hydrogen bonds were formed in three pyrimidine rings placed on the same plane. By comparing the measurements and simulations, almost all the absorption peaks appearing from 100 to 600 cm−1 could be assigned to torsional or skeletal vibrations of a pyrimidine ring. On the other hand, absorption peaks appearing in the THz range from 16.7 to 167 cm−1 were assigned to intermolecular vibrations.

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Optical absorption spectra in a frequency range from 0.5 to 5.0 THz were measured in several epoxy resin nanocomposites with and without co-addition of micro-sized fillers, aiming at obtaining important information on intermolecular interactions between filler and polymer. As a result, significantly large absorption appears when both micro-sized MgO and nano-sized SiO2 fillers were added in epoxy resin. Similar but smaller absorption is also found in an epoxy resin composite with nano-sized TiO2 fillers.

Broadband far-infrared absorption spectra were measured for pellets containing guanine or cytosine and an aqueous solution containing hairpin DNA with the two bases. When the solution was dried at 80 • C, the absorption increased around 540 cm −1 . Quantum chemical calculations were conducted by assuming models simulating one, two, and three molecules of each base and another model representing the hydrogen bonding between the two bases. By comparing the spectra acquired experimentally and numerically, it has become clear that almost all absorption peaks appearing in a range from 16.7 to 650 cm −1 are due to skeletal and intermolecular vibrations. Two vibrational levels at 527 cm −1 in guanine and 524 cm −1 in cytosine decrease if hydrogen bonds are formed. Assuming that the two modes are causal vibrations of the 540-cm −1 absorption, the spectroscopic experiment catches that hydrogen bonds between guanine and cytosine in DNA are dissociated around 80 • C.

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