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During the past 15 years, Expert's research has become increasingly oriented toward vibrational spectroscopy, particularly Fourier transform infrared (FT-IR) spectroscopy. In the early 1980s, he developed modern step-scan FT-IR instrumentation for photoacoustic and photothermal spectroscopy of surfaces and opaque or light-scattering solids. He and his colleagues are now applying this technique to a variety of time-resolved and phase-resolved infrared spectroscopy problems, as well as to photoacoustic spectroscopy. He and his colleagues have been the leaders in the (re)development of step-scan FT-IR techniques.

Expert has used attenuated reflectance (ATR) FT-IR spectroscopy to study molecular species on the surface of lithium electrodes in situ. This project is aimed at better understanding the formation and nature of the solid-electrolyte-interphase (SEI) in lithium batteries. The SEI is known to be an important factor in determining the rechargeability of these batteries. He has also used ATR as an alternative technique in other projects.


Expert has used diffuse reflectance spectroscopy (DRS) in conjunction with FT-IR as a complement to photoacoustic FT-IR, most extensively in the study of the reaction of SO2 gas with various particulate solids, such as CaO and CaCO3 used in dry scrubbing processes for removing sulfur from stack gases. This EPA-funded research has been successful in identifying intermediates and deducing mechanisms of reaction in this important process.

Expert currently uses infrared spectroscopy in various projects, exclusively as FT-IR. Most of these projects involve the study of time-dependent processes, and include observation of molecular reorientation processes on the sub-millisecond time scale when polymer films are subjected to modulated mechanical strain, and liquid crystals are subjected to modulated electric fields. He is also studying the photophysics of heme proteins and organometallic complexes by use of time-resolved infrared absorption. The principal instruments for these studies are step-scan FT-IR spectrometers.


In the past, both circular dichroism (CD) and circularly polarized luminescence (CPL) have figured prominently in Expert's research. These projects have involved cryogenic CD spectroscopy of chiral single crystals of transition metal complexes and solution CPL of lanthanide complexes of chiral crown ethers. His research in these areas is presently inactive, but his experience is extensive and recent.

Expert is actively pursuing phase-resolved infrared spectroscopy in connection with several projects. This is possible because of the development in his laboratory of step-scan FT-IR instrumentation, which he has been using now for over 15 years. Phase-resolved FT-IR projects include dynamic rheo-optical characterization of polymer films, electric field-induced reorientation dynamics of liquid crystals and liquid crystal polymers, as well as photoacoustic spectral depth profiling of laminar materials.


Expert has been active in photoacoustic spectroscopy (PAS) since before 1980 for the study of opaque and light-scattering materials. His initial interest was in the UV-visible-near IR spectral regions, but, since 1983, his work has been almost exclusively in the infrared (IR) region. Step-scan FT-IR has been very important to this research, because it allows the phase of the photoacoustic signal to be easily obtained. He has published extensively in the area of FT-IR PAS, particularly for spectral depth profiling of polymers and other dielectric materials. He has also developed in the area of FT-IR photothermal laser beam deflection (or mirage effect) spectroscopy to study surfaces in situ.


Expert has used Raman spectroscopy as a complimentary technique to infrared measurements.

Almost all of Expert's research during his 33-year career has involved molecular optical spectroscopy, earlier in the UV-visible-near IR spectral regions, and more recently in the mid IR. He also has considerable experience in electron spin resonance (esr) spectroscopy, and has some experience in nuclear magnetic resonance (nmr) spectroscopy. He is conversant with other methods of spectroscopy and their comparative strengths, weaknesses, and instrumentation.


Expert has worked extensively in the area of polarized light spectroscopy for over 30 years. This work has included cryogenic linear dichroism and circular dichroism (absorption) spectroscopy of single crystals of transition metal complexes, as well as circular dichroism spectroscopy of solutions of transition metal complexes, solution circularly polarized luminescence of lanthanide complexes of chiral macrocycles, and specular reflectance linear dichroism of single crystals.


Time-resolved (time-domain or impulse-response) spectroscopy (TRS) is closely related to phase-resolved (frequency-domain or modulation-demodulation) spectroscopy (PRS). In TRS, the sample is perturbed by a sudden impulse, and the response (change in the spectrum) is monitored as an explicit function in time. In PRS, the perturbation is modulated (usually sinusoidally), and the response is demodulated with a lock-in amplifier or digital signal processor. The time dependence is obtained from the phase-lag of the response with respect to perturbation. Expert uses step-scan FT-IR TRS in his work to investigate the photophysics of heme proteins and organometallic complexes, as well as for a complement to PRS studies of liquid crystal dynamics.

Expert's work in photothermal spectroscopy has been in the area of laser beam deflection at solid surfaces (the "mirage effect"). In the mirage effect, light absorbed by a solid generates a thermal gradient in the surrounding medium at the surface which is probed by a laser beam. Deflection of the probe beam as a function of wavelength yields the spectrum. This is an adjunct to photoacoustic spectroscopy (PAS), and is more useful on smooth impervious surfaces, whereas PAS is more adapted to porous materials.