Our research program is primarily focused on the following:
- Fundamental investigations of interactions between molecules designed to advance understanding and quantitative characterization of hydrogen bonding and related phenomena.
- Experimental development of quantum cascade laser and solid state non-laser Terahertz techniques to reveal fundamentally new information on intermolecular interactions.
- In collaboration with Dr. R. R. Lucchese, semi-empirical morphing methodologies are developed so that vibrationally-complete potentials can be generated capable of characterizing intermolecular properties to near spectroscopic accuracy as well as discovery of new weakly bound phenomena.
- Previously described instrumental developments are being directed to produce THz sensors capable of attomolar or even single molecule detection. Future applications will involve homeland security, medical diagnostics and monitoring, environmental pollution and other applications in analytical chemistry.
- Interdisciplinary collaborations at both national and international levels that enhance the careers of students in our group.
(i) Fundamental investigations into the nature of hydrogen bonds and related intermolecular interactions. Such interactions are important for their influence on the properties of gases, liquids and solids from a small molecule such as hydrogen bromide to intricate dynamics associated with DNA and protein folding. In collaboration with Dr. R. R. Lucchese, we have developed morphing methodologies that can generate semi-empirical functions capable of predicting the properties of prototypical interactions to an unprecedented near spectroscopic accuracy. This is achieved through transformation of initially generated ab-initio potential energy surfaces to accurately reproduce a wide and varied range of high resolution spectroscopic data for prototypical systems. Such spectroscopic data is generated using state-of-the-art spectroscopic techniques exploiting recently developed quantum cascade lasers and ultra-high resolution THz spectroscopic techniques developed in house. The exquisite resolution of the submillimeter co-axially configured molecular spectrometer was demonstrated in spectral studies of (HBr)2 and (HI)2 . The synergistic approach of combining high resolution spectroscopic techniques with morphing methodologies has recently been demonstrated in the ground state structure of (HI)2 that has been shown recently to give rise to an unexpected symmetric paired hydrogen bonded structure unlike any other (HX)2 (X=F, Cl, Br) dimer as well as having an anomalous structural isotope effect on mono-deuteration. Furthermore, 4-dimensional (4-D) morphing methodologies have also been used to predict another anomalous deuterium isotope effect in the ground state isotopic isomerization of OC-HI. Here, the ground state hydrogen bonded structure of OC-HI contrasts with the corresponding ground state van der Waals OC-ID structure, a fundamental phenomenon not considered before in non-covalent interactions. More recently, a CMM-RS methodology has been further refined to generate a 6-D vibrationally-complete PES for a hydrogen bonded interaction, OC-HF. This potential was morphed using only a four parameter fit to near spectroscopic accuracy for all currently available rovibrationally analyzed data (standard deviation of vibrational band origins < 0.017 cm-1). We are now especially interested in extending the application of such methodologies to hydrogen bonded interactions with increasingly higher dimensionality and with concurrent spectroscopic investigations for more general application of morphing.
(ii) Development of spectroscopic instrumentation and techniques. As an adjunct to our spectroscopic investigations, we custom construct spectroscopic instrumentation and related techniques. We have recently designed a multi-purpose frequency and phase stabilized submillimeter backward wave oscillator spectrometer. Currently, static gas phase sub-Doppler spectroscopy can be used to provide linewidths of < 16 kHz (5x10-7 cm-1) with precision of up to 15 Hz (5x10-10 cm-1). A sensitive co-axially configured supersonic jet version of this instrument has recently been completed with a linewidth <20 kHz and an accuracy of <1 kHz for molecular studies at less than 10 Kelvin. The spectrometer is now being upgraded for investigations in molecular interactions of significance in biological chemistry, pollution monitoring and reaction dynamics in the Terahertz gap up to 8.2 THz (262 cm-1) with continuous spectral coverage and unprecedented instrumental resolution of better than 20 kHz. In conjunction with this work, cavity enhanced methods are being developed with the object of ultrasensitive attomolar detection of molecules in the THz spectral region. We are also currently developing techniques that exploit the relatively high power characteristics of commercially available quantum cascade lasers for double resonance and electromagnetically induced transparency (EIT) studies in hydrogen bonded interactions.
(iii) State-specific molecular screening of diseases. State-specific molecular monitoring provides a unique and rapid approach to medical diagnostics. We are currently developing new analytical techniques and procedures based on the approaches discussed above that effectively constitute a breathalyzer for screening and diagnosis of lung cancer and other diseases. Our point-of-test non-invasive approaches involve both laboratory and pre-clinical investigation.
(iv) Environmentally compatible non-thermal surface wave plasma-based technologies for hazardous waste disposal. Since our group initiated the application of surface wave plasma (SWP) abatement for environmental purposes, we have been repeatedly surprised at its versatility for pollution mitigation. The unique properties of this traveling-wave plasma technology have been demonstrated to be particularly effective for destruction and removal (DRE) of PFCs and HFCs emitted into the atmosphere during 200 mm semiconductor manufacture. We are now focusing on fundamental investigations for modeling alpha and beta tests for 300 mm semiconductor process technologies and DRE of ozone-depleting CFCs.
Z. Wang, B.A. McElmurry, R.R. Lucchese, J.W. Bevan and L.H. Coudert, "Paired Hydrogen Bonds in the Hydrogen Halide Homodimer (HI)2", J. Chem. Phys. 134, 064317-064332 (2011).
L.A. Rivera-Rivera, Z. Wang, B.A. McElmurry, F.F. Willaert, R.R. Lucchese, J.W. Bevan, R.D. Suenram and F.J. Lovas, "A Ground State Morphed Intermolecular Potential for the Hydrogen Bonded and van der Waals Isomers in OC:HI and a Prediction of an Anomalous Deuterium Isotope Effect", J. Chem.Phys. 133, 184305-184318 (2010) .
L.A. Rivera-Rivera, R.R. Lucchese and J.W. Bevan, "A Four Dimensional Compound Model Morphed Potential for OC-HBr Complex", Chem. Phys. 12, 7258-7265 (2010).
L. H. Coudert, S. P. Belov, F. Willaert, B. A. McElmurry,R. R. Lucchese, J. W. Bevan, and J. T. Hougen, "Submillimeter Spectrum and Analysis of Vibrational and Hyperfine Coupling Effects in (HI)2", Chem. Phys. Letts 482, 180-188 (2009).
F.F. Willaert, B.A. McElmurry, R.R. Lucchese and J.W. Bevan, "Probing the Accuracy of the Isomerization Energy of the 3-D Morphed Potential of Ar-HBr", Chemical Physics Letters 460, 325-30 (2008).
B.A. Wofford and J.W. Bevan, "Current Status of Surface Wave Plasma abatement of Semiconductor Global Warming Emissions," Fut. Fab. International 11, 89-96 (2001).