Alkali band shift

The absorption band at 300 nm may also be associated with alkali ions, possibly the result of a trapped electron stabilized by an alkali ion. The band shifts to longer wavelengths when heavier alkali ions are present, and growth rates for the band show a definite dependence on the type of alkali (205,209). 

The UV spectra of the amide ion in crystalline alkali halides at 21 K consist of a main band with a shoulder at shorter wavelengths. The maximum of the main band shifts to... 

Polyacetylene can be electrochemically doped with any alkali-metal as done chemically. A high doping level gives rise to approximately the same new features which may depend somewhat on the cation inserted as a counterion. If we refer for example to the results shown in Fig. 5 (taken from ref. 15), we may notice that the additional bands shift downwards in frequencies when the cation size increases. 

The same type of vibration spectra is obtained for other heptafluorotantalates and heptafluoroniobates of alkali metals as well, with the degree of similarity depending to a certain degree on the nature of the second cation. The bands usually shift to the red when going from Li to Cs. This shift is related to a slight increase in the share of Ta-F bond covalence. 

Hisatsune and co-workers [290—299] have made extensive kinetic studies of the decomposition of various ions in alkali halide discs. Widths and frequencies of IR absorption bands are an indication of the extent to which a reactant ion forms a solid solution with the matrix halide. Sodium acetate was much less soluble in KBr than in KI but the activation energy for acetate breakdown in the latter matrix was the larger [297]. Shifts in frequency, indicating changes in symmetry, have been reported for oxalate [294] and formate [300] ions dispersed in KBr. 

There is an interesting similarity in the character of the solution absorption spectra of the isoelectronic ions Np3+ and Pu1 even though the absorption bands in Pu1 + are all shifted toward higher energies due to increases in both the electrostatic (Fk) and spin-orbit ( ) parameters, Table VI. We have also examined the spectra of complex alkali-metal Pu(IV)... 

After cocondensation of SiO (1226 cm 1) with alkali metal atoms like Na or K, new bands are detected at 1014 cm 1 (Na) or 1025 cm 1 (K). They can only be attributed to an SiO" anion because of the red shift of the SiO stretching vibration (with respect to that of uncoordinated SiO) and because of different isotopic splittings (28/29/30SiO, Si16/180) [21]. The formation of an ionic species M+(SiO) (M = Na, K) is in line with the results of quantum chemical calculations for the SiO anion (SiO d = 1.49 A, SiO" d = 1.55 A, "electron affinity" SiO + e + 1.06 eV —> SiO") [20]. Taking simple Coulomb interactions into consideration this species is very likely to have a strongly bent structure. The same situation occurs in gaseous NaCN (<(NaNC) = 81.2°) [22],... 

Risen et al. investigated cation—anion interactions using far IR spectroscopy (50—300 cm ) to study Nafion sulfonate membranes that were neutralized by cations in the series Na+, K+, Rb+, and Cs+ and the series Mg +, Ca +, Sr +, and Ba +, as well as the acid form." The spectra in this region for hydrated samples show a broad but well-defined band below 300 cm that is not present for the acid form. For both the monovalent alkali and divalent alkaline earth series, the band monotonically shifts to lower frequencies, f, such that foe where Mis the... 

Some generalizations have been made about the effect of various substituents on the absorption maxima and molar absorptivities (165). As expected, the absorption band around 280 nm is displaced to lower wavelengths when two methoxyls are replaced by a methylenedioxy group. The UV spectra of pavines are slightly affected by protonation on nitrogen (755). Similarly, quaternary species furnish UV spectra which closely resemble those of their tertiary counterparts (153). In some pavine bases such as norargemonine (13), the expected bathochromic shift on addition of alkali has not been observed (702). 

These spectra exist, characteristically, of bands which may be very broad or very narrow, and which may show vibrational structure. Examples of very broad bands without any structure at all, not even at very low temperatures, are found in the spectra of the F centre (an electron trapped at a halide vacancy in the alkali halides), and the tungstate (WO2-) group in CaW04. The spectral width may approach a value of 1 eV, and the Stokes shift of the emission band may be 2 eV. 

More surprisingly, however, are the striking variations observed in the potential dependence of as the cation is altered. For the heavier alkali cations, K" ", Rb- -, and Cs , one and sometimes two Vqj bands were commonly observed at each potential, whose frequencies shifted to lower values as the potential becomes less positive in the vicinity of the Fe (CN) e 3ylt formal potential, 200 mV vs SCE. (This is... 

Figure 17 presents the results of an FTIR spectroscopic study of the effect of salt concentration on the cmt of 70 mM SDS. As Mantsch et al. (4) have shown in similar work with alkali hexadecylsulfates, the cmt can be related to the sudden increase in frequency of the v9 CH2 bands as a function of temperature. The large increase in the gauche conformer content of the methylene chains of the surfactant tails as they "melt" at the cmt is responsible for this frequency shift. The effect of added salt is to raise the cmt of SDS, which is the cause of the "salting out" of this ionic surfactant at any given temperature. The cmt values, taken as the midpoint of the discontinuities in the frequency-temperature plots, agree well with those obtained by other means (14,54). 

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