Absorption bands position

Far-infrared absorption measurements gave an independent determination of the electron density from the position of the Frohlich mode near 9 meV ( 140 jum) a density of 2.3 X 1017 cm-3 was inferred. Other experiments on Sb-doped Ge and pure germanium irradiated at different powers showed appreciable changes in absorption band positions and shapes. Rose et al. 

Annelation on to a benzene ring increases considerably the complexity of the spectra, and indole has absorptions at 216 (4.54), 266 sh (3.76), 270 (3.77), 276 (3.76), 278 (3.76) and 287 (3.68) nm in ethanol solution. Because of the widespread occurrence of the indole ring system in nature and the sensitivity of absorption band position and intensity to substitution type, considerable use has been made of electronic spectroscopy in the past for structure identification. An extensive tabulation of data, primarily for monosubstituted derivatives, is available (71PMH(3)67,p.94). As expected, whereas the effects of alkylation are comparatively slight, introduction of groups capable of mesomeric interaction with the indole it -system may cause profound changes in the appearance of the spectrum representative examples are given in Table 24. 

Fig. 10.6 Extrapolation to 0 K of the Cm infrared absorption band position. This is the case of the F (4) band, the pentagonal pinch mode. The intercept at 0 K occurs at 1430.9 cm-1...

Triplet absorption spectra of o-quinodimethane bis-adducts exhibit some differences to the corresponding monoadduct. The absorption band positions are only less affected, whereas the lifetime strongly differs between the regioisomers. Also, the initial absorbance differs noticeably, which may be associated with the quantum yield of intersystem crossing from Si to Tx [110],... 

Table 13.1 Infrared Absorption Band Positions ofVarious Carbonyl Groups...

The above series in general is similar to the ligand nephelauxetic series observed in the case of d-transition metals. The greatest nephelauxetic effect has been observed in sulphides [46], cyclopentadienides [47], and oxides [48] of lanthanides. However, attempts to formulate a common and general nephelauxetic series for the lanthanide series have been futile using aquo ions as reference standards. In the case of lanthanide complexes with the same ligand in aqueous solutions, the absorption band positions of light and heavy lanthanides shift in different directions. This unusual behavior of complexes may be due to the differences in structure of aquo ions and the complexes. 

Several electronic absorption-band positions of these complexes are given ... 

Huguenin R. L. and Jones J. L. (1986) Intelligent information extraction from reflectance spectra absorption band positions. J. Geophys. Res. 91, 9585-9598. 

Sugimoto et al.184) pointed out that the absorption band position cannot be fitted with calculated values if no ionic chromophore structure is assumed. They also... 

Although the calculations of the transition energies of different tautomeric forms of molecules have been performed in a few cases, the discussion has been restricted to the difference in electronic absorption band positions and not to the change in relative stabilities of the tautomers caused by electronic excitation. The latter problem, however, has been the subject of a few theoretical considerations for nucleic acid base pairs. Most of these studies were motivated by the need for a potential function for double proton transfer between nucleic acid bases that would allow calculation of proton tunneling probabilities for the Lowdin model of mutagenesis (Lowdin, 1965). 

Here the difference in solvation energy of two tautomers in their excited state is defined as Af a,b( ) = Af A>B + hc( Ava - A B), where Ai> = f(v) -Hs) indicates the shift of the 0-0 (or maximum) absorption band positions of the tautomers on going from vapor phase to solution. 

As early as 1992, Fastow et al. [66] reported the IR results for CO and NO adsorption on Cgg. The spectra recorded at 77 K for CO adsorbed on Cgg films, which have led to further analyses being carried out, are reproduced in Fig. 14.8. Two partially overlapping absorption bands, positioned at 2135 1 and 2128 lcm , can be observed. The appearance of two bands suggests that CO adsorbs on two different sites on the Cgg surface. The large spectral shifts regarding gas-phase frequency (2153 cm ) indicate that the interaction is relatively strong. A similar conclusion was drawn from NO adsorption, which also showed a multiplicity on the two absorption bands, an indication that NO is adsorbed on its dimer form in two different sites. Shortly after this work, IR spectra for CO2 and N2O adsorption on Cgg, graphite and diamond films were also studied [67]. In this case, only one adsorption site was... 

Yasui et al. (1965 Yasui, 1965) studied the CD spectra of copper-amino acid complexes in more detail and showed that copper complexes with l-amino acids in water exhibit four Cotton effects in the region of the d-d absorption band positive at 830 and 730 nm and negative at 635 and 565 nm. The CD curves of the complexes of proline, hydroxyproline, and histidine are considerably different from those of other amino acid complexes for which the main CD band at ca. 630 nm shows the opposite positive Cotton effect. It was suggested that the vicinal effect of the asymmetric a-carbon atom is stronger than that of the asymmetric j -carbon atom (L-threonine and L-allothreonine) and thus determines the sign of the Cotton effects. 

Absorption band positions are given in wave number units (v), which are expressed as cm , or alternatively in wavelength units (A), in microns (fi) (also called micrometers, jum). The true unit of frequency (v) is measured in reciprocal seconds (sec ). The relations of these units to each other are v [cm ]= 1/A[cm] = 10,000/A [ji] V = c/A thus, 2000 cm = 5.00 ju, and 1250 cm = 8.00ju. The reader is referred to Appendix 2 for a Table of Reciprocals, which is useful in converting wavelengths to wave numbers, and vice versa. 

Relevant parameters are summarized in Table 12. A comparison between experimental and calculated uv absorption band positions i i ,(x,ir ) is given in Section II.E (Table 21). 

IR absorption bands in amorphous solids are rather broad, with extensive overlap. Direct identification and quantification of the numerous oxidation products, most often of similar chemical structures, in a degraded polymer are difficult. More precise conclusions about the nature of absorbing species can be obtained by selective chemical derivatization. Selective modification of functional groups with reactive gases, such as SF4, NH3, SO2, or NO, results in a shift in absorption band positions, which can then be compared with model compounds to allow for a better chemical assignment of the absorbing species (Table 15.3) [13]. 

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