Infrared absorption, origin

Most of the many modes of a-Ss have been assigned to their symmetry class. However, some strong infrared absorptions (V4 240 cm V5 470 cm ) and weak Raman lines (Vn 250 cm ) as well as signals originating from accidental degeneracies (e.g., Vi, V5, and Vy at around 475 cm ) were difficult to assign. 

Figure 2. Infrared absorption spectra of the 8.4A hydrate (A), the 8.6A hydrate (B), the 10A hydrate (C)i and the original kaolinite used to synthesize the three hydrates (D).

Biological, chemical. X-ray diffraction, infrared absorption, e.s.r., n.m.r., luminescence, and quantum studies show that dimer formation is universally observed in irradiated frozen solutions of thymine, thymidine, uridine, thymidylic acid and related compounds, and in DNA [560—576]. The purines of DNA, on the other hand, are little affected [577, 578]. Thymine dimers obtained in frozen solution can be converted to the original monomers by ultraviolet... 

Minshall and Helson (7) of the Dominion Department of Agriculture at Ottawa, Canada, have studied the physiological action of petroleum naphtha on carrots, parsnips, and several weeds including mustard. They used infrared absorption apparatus, and by means of readings taken at 10-second intervals following oil application, determined that photosynthesis ceased abruptly for all plants studied. With parsnips, photosynthesis was resumed within 30 minutes after application it was one third of norm at the end of 3 hours, and at the end of 48 hours reached approximately the original rate before treatment. Parsnips did not wilt following treatment. The common mustard plant had a... 

The data manipulating capability of a computerized infrared spectrometer allows the spectroscopist to delve more deeply into the structural origin of the infrared absorptions by using data processing techniques to purify, manipulate, and correlate the spectra. If one can systematically vary the relative amounts of various structural contributions, absorbance subtraction can be used to isolate the spectral contributions of the structural components. 

Fig. 4.7 Positions of the band origins of the infrared absorption spectrum of a diatomic molecule.

Bokobza, L. (2002). Origin of near-infrared absorption bands. In Near-Infrared Spectroscopy Principles, Instruments, Applications, Siesler, H. W., Ozaki, Y., Kawata, S., and Heise, H. M., eds., Wiley-VCH, Weinheim, Germany, pp. 11-39. 

Achhammer (2) and co-workers, who originally studied the effect of ultraviolet radiation on this polymer, reported that on exposure to a sunlamp the infrared absorption bands increase in the regions of 2.8/u. and... 

Chemical analysis of the residual material yields the results given in Table I. The notable data are the halogen content and the limited availability of the calcium for base exchange. Infrared absorption peaks found for the clean and reacted material are shown in Table II. The important features are the appearance of a band ascribable to Si-F bonds and a shift in an Si-OH band. X-ray diffraction photographs indicate only a small increase in amorphous background and retention of the greater part of original pattern. 

Although direct access to the (10000), (01000), and (00010) levels from the (00000) ground-state level by infrared absorption is thus rigorously forbidden by symmetry, access from molecules in the (00010) or (00001) levels can be symmetry allowed. For example F(OOOOl) X F(IOOOO) = n X 2 = n = r(/t ), and so the transition between these levels, termed a difference band, — v, is not formally forbidden. As can be seen in Fig. 1, the frequency (vi - v ) can be added to the fundamental frequency to give the evarf value of the (lOOOO)-(OOOOO) spacing. Similarly, the V2 and 3 difference bands are infrared-active and can be combined with and v, to deduce V2 and v, respectively. Such difference bands are detectable for acetylene but will of course have low intensity because they originate in excited levels that have a small Boltzmann population at room temperature. The intensity of such bands increases with temperature, hence they are also termed hot-band transitions. 

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