Selection rules spectral band intensities

Band intensities spectral, 249 selection rules, 244 Band widths spectral, 246 temperature effects, 248 Barium, pentakis(diacetamide)-stereochemistry, 99 Bathocuproine absorptiometry, 550 Bathophenanthroline absorptiometry, 550... 

In describing an electronic transition usually one specifies the energy, which describes the spectral region in which the band lies, and the intensity, which is a measure of the transition probability. The former is treated in terms of the Franck-Condon principle while the absolute intensity depends on transition moments which involve certain selection rules derived from quantum mechanics. 

Theoretical calculation of the frequencies of the normal modes of vibration is possible and has been demonstrated for moderately complex molecules such as acetazolamide [34]. This facilitates assignment of the observed spectral bands beyond what may be possible by comparison with correlation tables and manual interpretation. The ability to predict the visual appearance of IR and Raman spectra is, however, more challenging since the inclusion of selection rules to ascertain which bands will be IR or Raman active and the calculation of their intensity must be considered. 

SERS of amino acids, polypeptides and proteins For a successful interpretation of the SERS spectra of proteins it is essential to have detailed information about the SERS behaviour of their monomeric units and simple models. It is reasonable to expect that the intensity of their SERS bands depends on the orientation of the protein molecule with respect to the surface. On the basis of a careful assignment of spectral bands and surface selection rules proposed by Moskovits [63, 80, 81], the orientation of amino acids adsorbed on the surface of colloidal silver was predicted [82-84]. 

Spectral bands of an aquated lanthanide ion arising from vibronic contributions were reported first by Haas and Stein (1971) in their study of the emission spectrum of aquated Gd. These bands are termed vibronic because they arise from a simultaneous change in the electronic state of the metal ion and the vibrational state of a coordinated ligand. Stavola et al. (1981) noted additional examples of such bands and presented a theoretical model based on the importance of electronic factors for calculating the intensities of lanthanide-ion vibronic transitions. Their theoretical model also predicts selection rules for such transitions. The intensities of observed bands assigned by these workers as being vibronic typically were at least 50 times weaker than the parent purely electronic band. Faulkner and Richardson (1979) have... 

Any spectrum can consist of any or all combinations of the aforementioned mode types. The range of possibilities for a given ordered polymer structure is determined solely by the symmetry properties of the polymer. However, the picture may be distorted by the limited spectral sensitivity of the Raman and IR instrumentation (in other words, a Raman or IR vibrational mode can be expected theoretically, but the intensity of the mode is so low that it is not observed experimentally). Instruments yielding high signal-to-noise ratios will minimize this problem. Another complication is the presence of multiple or disordered structures (which have no specific selection rules) that cause deviations from the pure mode selection rule requirements of the perfect chain. The spectral bands that are associated with minor amounts of irregular structures are weak and variable in intensity from sample to sample, which makes their detection possible in some cases. 

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