CAREER: Terahertz Spectroscopy of Molecular Solids: Experiment and Theory

Syracuse University, Syracuse NY

Investigators

Abstract

In this award, Dr. Timothy Korter from Syracuse University, together with his graduate students, will employ time-domain terahertz (THz) vibrational spectroscopy to probe interactions between molecules in the solid state. The vibrations are strongly influenced by the molecular environment which provides information about the intermolecular potential energy surfaces which in turn are related to macroscopic chemical properties such as phase transitions. Dr. Korter plans to investigate two important classes of materials - crystalline pharmaceuticals and solid-state energetic materials. Due to their complicated structures influenced by hydrogen bonding, crystal packing and the presence of enantiomers, the THz vibrational spectra are exceedingly complex, and interpretation is only possible through integration of predictive methods. Density functional theory and ab initio modeling combined with careful experimentation will be instrumental in understanding the origins of the spectral features observed. Structural analysis will be complemented through techniques such as NMR spectroscopy, X-ray diffraction, and Raman spectroscopy. Collaboration with Dr. Brown from UCSB will provide access to spectral features below the resolution limit available in Dr. Korter's laboratory. The educational plan consists of developing museum displays for the Milton J. Rubenstein Museum of Science and Technology in Syracuse, NY. These displays are aimed at achieving an understanding and appreciation of different time scales ranging from seconds to femtoseconds, the timescale at which Dr. Korter performs his experiments. The displays will be interactive and visually appealing to draw the visitor to them, and then actively engage him or her. The PI plans to liaise with specialists in the field to maximize their educational value. Terahertz (THz) radiation can see through clothing, plastic and paper which make scanners based on this technology good candidates to detect concealed weapons in airport security. Unlike X-rays, THz rays are very low in energy and can be applied without health risks. Their ability to see through materials like plastics makes it possible to characterize the content of a container without opening it. In this award, Dr. Korter from Syracuse University will uncover the identifying features of explosives and illicit drugs when subjected to THz radiation. Each individual material gives rise to a very unique pattern when a plot is generated of how much of the THz radiation is reflected or absorbed. These patterns are so complex that Dr. Korter will also have to develop theoretical calculations to predict how a material is expected to react to the radiation, and then compare these features with the experimental patterns. Once these patterns are understood, they can be used to identify illicit materials in routine screenings. When subjecting the materials to THz radiation, Dr. Korter does not irradiate them continuously but in very, very short pulses which allows him to extract information on how the material is reacting to such a short perturbation. The response is unique for each material. The pulses are on the order of femtosecond duration, or the millionth fraction of a billionth of a second. This is almost impossible for the human mind to grasp - therefore, Dr. Korter will develop interactive displays for museums that help the visitor in developing a sense for ultra-short time scales.