Theoretical Underpinnings


Figure: HNO3 Spectrum. A series of
blow ups in both frequency and sens-
itivity of the spectrum of HNO3. The
~45 GHz scan shown at the top was
recorded in a single ~1 sec scan, with
the 300 MHz segment shown at the
bottom recorded in ~0.01 sec.


A number of excellent books and texts discuss the theoretical underpinnings of rotational spectra in detail. These include the early classic texts of Gordy, Smith, and Trambarulo [1]. Here we will briefly discuss the underlying physics and its implications so that we can discuss the general character of THz spectroscopy and its applications. The interested reader is referred to the aforementioned texts for methods of detailed calculation.

The physics that underlies spectroscopy in the THz region is very favorable. Briefly stated, THz spectroscopy is orders of magnitude more sensitive than spectroscopy in the adjacent microwave region, provides orders of magnitude greater resolution than infrared spectroscopy (especially for experimental systems of comparable size and complexity) because of smaller Doppler widths, and provides absolute quantitative analysis traceable to fundamental theory. Figure: HNO3 Spectrum shows a series of blow ups in both frequency and sensitivity to provide a perspective. The ~45 GHz scan shown at the top was recorded in a single ~1 sec scan, with the 300 MHz segment shown at the bottom recorded in ~0.01 sec.

Papers that include additional theoretical detail:

  1. De Lucia, F. C., Helminger, P., Cook, R. L. & Gordy, W. Submillimeter Microwave Spectrum of H216O Phys. Rev. A: At., Mol., Opt. Phys. 5, 487-490 (1972). - Water as an example of SMM/THz rotational spectroscopy: Experimental and theoretical approaches Google Scholar
  2. De Lucia, F. C., Helminger, P. & Gordy, W. Submillimeter-Wave Spectra and Equilibrium Structures of the Hydrogen Halides Phys. Rev. A: At., Mol., Opt. Phys. 3, 1849-1857 (1971). - Rotational spectroscopy of the hydrogen halides: Fundamental diatomic relations Google Scholar
  3. Manson, E. L., Clark, W. W., De Lucia, F. C. & Gordy, W. Millimeter Spectrum and Molecular Constants of Silicon Monoxide Phys. Rev. A: At., Mol., Opt. Phys. 15, 223-226 (1977). - Rotational spectroscopy of gas phase SiO Google Scholar
  4. Helminger, P., Bowman, W. C. & De Lucia, F. C. A Study of the Rotational-Torsional Spectrum of Hydrogen Peroxide Between 80 and 700 GHz. J. Mol. Spectrosc. 85, 120-130 (1981). De Lucia, F. C., Herbst, E., Anderson, T. & Helminger, P. The Analysis of the Rotational Spectrum of Methanol to Microwave Accuracy J. Mol. Spectrosc. 134, 395-411 (1989). - Rotational spectrscopy and analysis techniques for the prototype internal rotors CH3OH and HOOH J. Mol. Spectrosc. 85, 120-130 (1981). De Lucia, F. C., Herbst, E., Anderson, T. & Helminger, P. The Analysis of the Rotational Spectrum of Methanol to Microwave Accuracy%22" title="Search Google Scholar for this entry">Google Scholar
  5. Plummer, G. M., Herbst, E., De Lucia, F. C. & Blake, G. A. The Millimeter and Submillimeter Laboratory Spectrum of Methyl Formate(HCOOCH3) in Its Ground Symmetric Torsional State. Astrophys. J., Suppl. Ser. 55, 633-656 (1984).Plummer, G. M., Herbst, E., De Lucia, F. C. & Blake, G. A. The Laboratory Millimeter-Wave Spectrum of Methyl Formate in its Ground Torsional E. State Astrophys. J., Suppl. Ser. 60, 949-961 (1986). - Spectroscopy and analysis of the astrophysical 'weed', methyl-formate Astrophys. J., Suppl. Ser. 55, 633-656 (1984).Plummer, G. M., Herbst, E., De Lucia, F. C. & Blake, G. A. The Laboratory Millimeter-Wave Spectrum of Methyl Formate in its Ground Torsional E. State

References

  1. Gordy, W., Smith, W. V. & Trambarulo, R. F. Microwave Spectroscopy (John Wiley and Sons, 1953). Google Scholar
  2. Townes, C. H. & Schawlow, A. L. Microwave Spectroscopy (McGraw-Hill Dover Publications, Inc., 1955). Google Scholar
  3. Carrington, A. Microwave Spectroscopy of Free Radicals (Academic Press, 1974). Google Scholar
  4. Kroto, H. W. Molecular Rotation Spectra (Wiley, 1975). Google Scholar
  5. Gordy, W. & Cook, R. L. Microwave Molecular Spectra Techniques of Chemistry 18, 929 (John Wiley & Sons, 1984). Google Scholar
  6. Cook, R. L. Macmillan Encyclopedia of Chemistry (Macmillan Press, 1997).
  7. Cook, R. L. Encyclopedia of Physical Science and Tecnology (Meyers, R. A.) (Academic Press, 2000).