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Continuous-Wave Terahertz Spectroscopy of Plasmas and Biomolecules

Published

Author(s)

David F. Plusquellic, T M. Korter, Gerald T. Fraser, R J. Lavrich, Eric C. Benck, C R. Bucher, Angela R. Hight Walker, J L. Domenech

Abstract

Continuous-wave linear-absorption spectroscopy based on THz radiation generated by solid-state photomixers has been applied to the investigation of the dynamics of biomolecules in polyethylene matrices and to line shape studies of HF for diagnostics of semiconductor etching plasmas. The THz spectra of biotin and myoglobin have been obtained using a variable-temperature, cryogenic sampling system. The spectrum of biotin displays a small number of discrete absorptionsover the temperature range from 4.2 K to room temperature while the spectrum of myoglobin has no obvious resonance structure at the > 10 % fractional absorption level. Spectral predictions from the lowest energy ab initio conformations ofbiotin are in poor agreement with experiment, suggesting the need to include condensed-phase environmental interactions for qualitative predictions of the THz spectrum. Vibrational anharmonicity is used to model the line shapes that result from drastic changes in vibrational state populations of biotin over this temperature range. Anharmonicity factors ([chi]e[omega]e/[omega]3) at the levels of 1 % to 2 % are needed for most but not all of the observed resonances and illustrate their important for refining model predictions. Application of the photomixer system to line shape studies of HF in etching plasmas has permitted the determination of its translational temperature and collision-broadened width under different operating conditions. These results will aid in understanding the chemistry of industry-standard fluorocarbon and oxygenated fluorocarbon etching plasmas.
Citation
Continuous-Wave Terahertz Spectroscopy of Plasmas and Biomolecules
Volume
2
Issue
No. 4
Publisher Info
Terahertz Sensing Technology Emerging Scientific Applications and Novel Device Concepts; Chapter 10. (World Scientific),

Keywords

biotin, cryogenic samples, CW THz spectroscopy, far-infrared myoglobin, semiconductor etching plasma diagnostics, THz spectra of biomolecules, vibrational anharmonicity

Citation

Plusquellic, D. , Korter, T. , Fraser, G. , Lavrich, R. , Benck, E. , Bucher, C. , Hight, A. and Domenech, J. (2004), Continuous-Wave Terahertz Spectroscopy of Plasmas and Biomolecules, Terahertz Sensing Technology Emerging Scientific Applications and Novel Device Concepts; Chapter 10. (World Scientific), (Accessed August 14, 2022)
Created March 1, 2004, Updated February 17, 2017