Principles of molecular spectroscopy

The electromagnetic radiation emitted or absorbed by the substances under investigation is the subject of the oscillation-rotation (molecular) spectroscopy. In this section, the main attention is concentrated on molecular spectroscopy near and within the optical range of frequencies. 

Emission of the radiation quanta or their absorption is defined by energy transitions. Therefore, the basis of all spectroscopy methods is the discontinuity of energy spectrum and the mutual position of energy levels. Of course, this is only a general treatment many factors playing an important role in spectroscopy remain outside our discussion. 

Naturally, the best effect in the interaction of radiation with matter can be reached in the case when the energy of radiation quanta used coincides in order of values with energy transitions. Therefore, we will consider that range of quanta energy complies with that of energy transition on the basis of the data given in Table 5.3. 

In order to evaluate the oscillatory energy levels, it is necessary to know their intrinsic frequencies. Experiments show that they are 10 -10 Hz. Correspondingly, the emission frequency belongs to the IR radiation region and the wavelengths are 10 -10 m. 

The purely rotational frequencies he in the frequency range dependent on the molecule s rotational constant (7.8.13). Estimations show that B == (10 /10 ) == 10 J or 10 —10 eV. This corresponds to the wavelength A = 10 m, which corresponds to a microwave frequency far from the optical range. 

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Principles of Molecular Spectroscopy Quantized Energy States... 

PRINCIPLES OF MOLECULAR SPECTROSCOPY QUANTIZED ENERGY STATES... 

K. K. Liang, R. Chang, M. Hayashi, S. H. Lin, Principles of Molecular Spectroscopy and Photochemistry, Chung-Hsin University Press, Taichung, Taiwan, 2001. 

Despite the fact that signals from molecules may be coming from thousands of light years away, a quantitative analysis can be performed on interstellar gas through the use of radio telescopes and their remote sensing capabilities. Such telescopes at first glance may seem an odd tool for a chemist, but these instruments basically exploit fundamental principles of molecular spectroscopy in a manner similar, but not identical, to a laboratory spectrometer. 

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