Applications and Impact of THz Spectroscopy

High resolution THz spectroscopy has had a major impact on many important fields of science and technology. The earliest studies in this region were of species such as H2O, O2, NO, CH3F, and OCS and served to both establish spectroscopic methodologies and to provide basic information about molecular structure and interactions [1].

Because the strength of the interactions between electromagnetic radiation and molecular rotation peaks sharply in the THz, this spectral region has also been well suited for the study of reactive species such as free radicals [15].

A variety of spectroscopically based remote sensing applications has grown out of this more basic work. Of these, two have become of major importance. The first is the study of the chemical processes in the upper atmosphere which are important in ozone formation and destruction [26]. We will discuss each of these in more detail below.

Because of these and other applications (e. g. the modeling of atmospheric propagation) the spectroscopic properties of virtually all of the important atmospheric and astronomical species have been collected into data bases. These data bases have become the standard for many applications and play an important role in the development of the spectral region. The Submillimeter, Millimeter, and Microwave Spectral Line Catalog has been maintained by the Jet Propulsion Laboratory for many years [6]. Likewise, the HITRAN Molecular Spectroscopic Database has been maintained by the Air Force [7]. While the latter began primarily as an infrared database, the growth in both infrared and submillimeter experimental technologies has been such that for many molecular species the best spectral data base results from a weighted fit of infrared and microwave data to a theoretical model.

Although most of the spectroscopic work in this spectral region historically has been referred to as millimeter and submillimeter spectroscopy, in this chapter we will for the most part use the term THz. An interesting study of the relationships among the communities that work in this spectral region can be done by using an Internet search engine to explore 'THz' and 'submillimeter' Boolean combined with 'spectroscopy'.

References

  1. King, W. C. & Gordy, W. One to Two Millimeter Wave Spectroscopy. I Phys. Rev. 90, 319-320 (1953). Google Scholar
  2. Burrus, C. A. & Gordy, W. One-to-Two Millimeter Wave Spectroscopy. II. H2S Phys. Rev. 92, 274-277 (1953). Google Scholar
  3. King, W. C. & Gordy, W. One-to-Two Millimeter Wave Spectroscopy. IV. Experimental Methods and Results for OCS, CH3F, and H2O Phys. Rev. 93, 407-412 (1954). Google Scholar
  4. Gordy, W. Microwave Spectroscopy in the Region of 4-0.4 Millimeters Pure Appl. Chem. 11, 403-434 (1965). Google Scholar
  5. De Lucia, F. C. Molecular Spectroscopy, Modern Research 2, 73-92 (1976).
  6. Pickett, H. M., Poynter, R. L., Cohen, E. A., Delitsky, M. L., Pearson, J. C. & Müller, H. S. P. Submillimeter, Millimeter, and Microwave Spectral Line Catalog J. Quant. Spectrosc. Radiat. Transfer 60, 883-890 (1998). Google Scholar
  7. Helminger, P. & De Lucia, F. C. Pressure Broadening of Hydrogen Sulfide J. Quant. Spectrosc. Radiat. Transfer 17, 751-754 (1977). Google Scholar
  8. Pickett, H. M. Determination of Collisional Linewidths and Shifts by a Convolution Method Appl. Opt. 19, 2745-2749 (1980). Google Scholar
  9. Bauer, A., Godon, M., Kheddar, M., Hartmann, J. H., Bonamy, J. & Robert, D. Temperature and Perturber Dependences of the Water-Vapor 380 GHz-Line Broadening J. Quant. Spectrosc. Radiat. Transfer 37, 531-539 (1987). Google Scholar
  10. Goyette, T. M., De Lucia, F. C., Dutta, J. M. & Jones, C. R. Variable Temperature Pressure Broadening of the 41,4 - 32,1 Transition of H2O by O2 and N2 J. Quant. Spectrosc. Radiat. Transfer 49, 485-489 (1993). Google Scholar
  11. Messer, J. K. & De Lucia, F. C. Measurement of Pressure-Broadening Parameters for the CO-He System at 4 K Phys. Rev. Lett. 53, 2555-2558 (1984). Google Scholar
  12. Pearson, J. C., Oesterling, L. C., Herbst, E. & De Lucia, F. C. Pressure Broadening of Gas Phase Molecular Ions at Very Low Temperature Phys. Rev. Lett. 75, 2940-2943 (1995). Google Scholar
  13. Ball, C. D. & De Lucia, F. C. Direct Measurement of Rotationally Inelastic Cross Sections at Astrophysical and Quantum Collisional Temperatures Phys. Rev. Lett. 81, 305-308 (1998). Google Scholar
  14. Winnewisser, M., Sastry, K. V. L. N., Cook, R. L. & Gordy, W. Millimeter Wave Spectroscopy of Unstable Molecular Species II. Sulfur Monoxide J. Chem. Phys. 41, 1687-1691 (1964). Google Scholar
  15. Evenson, K. M., Saykally, R. J., Jennings, D. A., Curl, R. F. & Brown, J. M. Far Infrared Laser Magnetic Resonance Chemical and Biochemical Applications of Lasers V, (Academic, 1980). Google Scholar
  16. Charo, A. & De Lucia, F. C. The Millimeter and Submillimeter Spectrum of HO2: The Effects of the Unpaired Electronic Spin in a Light Asymmetric Rotor J. Mol. Spectrosc. 94, 426-436 (1982). Google Scholar
  17. Woods, R. C., Dixon, T. A., Saykally, R. J. & Szanto, P. G. Laboratory Microwave Spectrum of HCO+ Phys. Rev. Lett. 35, 1269-1272 (1975). Google Scholar
  18. van den Heuvel, F. C. & Dynamus, A. Observation of Far-Infrared Transitions of HCO+, CO+, and NH2+ Chem. Phys. Lett. 92, 219-222 (1982). Google Scholar
  19. De Lucia, F. C., Herbst, E., Plummer, G. M. & Blake, G. A. The Production of Large Concentrations of Molecular Ions in the Lengthened Negative Glow Region of a Discharge J. Chem. Phys. 78, 2312-2316 (1983). Google Scholar
  20. Busarow, K. L., Blake, G. A., Laughlin, K. B., Cohen, R. C., Lee, Y. T. & Saykally, R. J. Tunable Far-Infrared Laser Spectroscopy in a Planar Supersonic Jet: The S Bending Vibrations of Ar-H35Cl Chem. Phys. Lett. 141, 289-291 (1987). Google Scholar
  21. Marshall, M. D., Charo, A., Leung, H. O. & Klemperer, W. Characterization of the lowest-lying P bending state of Ar-HCl by far infrared laser-Stark spectroscopy and molecular beam electric resonance J. Chem. Phys. 83, 4924-4933 (1985). Google Scholar
  22. De Lucia, F. C. The Study of Laser Processes by Millimeter and Submillimeter Microwave Spectroscopy Appl. Phys. Lett. 31, 606-608 (1977). Google Scholar
  23. Skatrud, D. D. & De Lucia, F. C. Dynamics of the HCN Discharge Laser Appl. Phys. Lett. 46, 631-633 (1985). Google Scholar
  24. Everitt, H. O., Skatrud, D. D. & De Lucia, F. C. Dynamics and Tunability of a Small Optically Pumped CW Far-Infrared Laser Appl. Phys. Lett. 49, 995-997 (1986). Google Scholar
  25. Chance, K. V., Johnson, D. G., Traub, W. A. & Jucks, K. W. Measurement of the Stratospheric Hydrogen Peroxide Concentration Profile using Far Infrared Thermal Emission Spectroscopy Geophys. Res. Lett. 18, 1003-1006 (1991). Google Scholar
  26. Waters, J. W. Atmospheric Remote Sensing by Microwave Radiometry (1993). Google Scholar
  27. Carli, B. & Park, J. H. Simultaneous Measurement of Minor Stratospheric Constituents with Emission Far-Infrared Spectroscopy J. Geophys. Res.: Atmos. 93, 3851 (1988). Google Scholar
  28. Herbst, E. Chemistry in the Interstellar Medium Annu. Rev. Phys. Chem. 46, 27-53 (1995). Google Scholar
  29. Winnewisser, G. & Pelz, G. C. The Physics and Chemistry of Interstellar Molecular Clouds (Springer-Verlag, 1995). Google Scholar