The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient and a broad bandwidth in the low THz frequency region (13–130 cm−1), the intramolecular vibrational modes of the alkyl-chain part of an imidazolium cation with a relatively small absorption coefficient in the mid THz frequency region (130–500 cm−1), the intramolecular skeletal vibrational modes of an imidazolium ring affected by the interaction between the imidazolium ring, and a halogen anion with a relatively large absorption coefficient in a high THz frequency region (500–670 cm−1). Interesting spectroscopic features on the interaction between imidazolium cations and halogen anions was also obtained from spectroscopic studies at IR frequencies (550–3300 cm−1). As far as the frequency of the intermolecular vibrational mode is concerned, we found the significance of the reduced mass in determining the intermolecular vibration frequency.
Terahertz spectroscopy has rapidly progressed, and is being applied to various research fields as a new non-invasive examination method. Scientific analysis is important for the conservation of art, as it can help to reveal the history of a work and to determine the proper materials for its restoration. Mid-infrared spectroscopy and X-ray analysis are currently used to identify organic and inorganic materials, respectively. Terahertz spectroscopy is expected to identify composites themselves, and to give clear and direct information for art conservation. We have collected terahertz spectra of various historical and modern materials, and found that terahertz spectroscopy can distinguish the pigments, binders and their mixtures. The experimental results prove that terahertz spectroscopy as a new non-invasive examination method can contribute to art history and to restorations. The material database can also contribute to other fields such as earth science, the printing industry, and the food and pharmaceutical research fields.
Terahertz (THz) spectra were obtained for polylactide, and they were analyzed by numerical calculations based on density functional theory. An absorption band was observed at approximately 50 cm À1 , which becomes larger when the THz electric field is parallel to the sample drawing direction. An absorption peak with a similar directional dependence appears at approximately 40 cm À1 in the simulation, which is due to normalmode molecular vibrations parallel to the molecular helix. Since the 50 cm À1 absorption decreases with an increase in crystallinity and the permittivity shows a step-like decrease, the molecular vibrations responsible for the 50 cm À1 band seem to be subjected to strong damping in amorphous regions. On the other hand, another absorption peak at 65 cm À1 with a positive absorption dependence on the sample's crystallinity is likely to be due to lattice vibration, since it does not appear in the calculations, which only deal with intramolecular vibration.
Terahertz (THz) technology is a focus of attention in research on applied optics. We have applied THz spectroscopy and THzimaging method to text recognition of a medieval manuscript made from sheepskin. Based on the database which contains more than 200 spectra of art materials, the red ink on the manuscript was estimated as Cinnabar. The red ink text and stains on the text were successfully distinguished by the THz-Time Domain Spectroscopy (TDS) imaging with a component spatial pattern analysis. THz spectroscopy can be used as a non-invasive analysis method for conservation science of cultural properties.
scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.