Shifts in band positions

Amides have a very strong tendency to self-associate by hydrogen bonding, and the appearance of the spectrum is very much dependent on the physical state of the sample. Considerable shifts in band positions can occur on passing from a dilute solution to a solid, thus N—H and C=0 stretching bands show a marked shift to lower frequency while the N—H bending (amide II) band moves to higher frequency. 

Spectroscopic studies of Co (II) derivatives of stellacyanin, plastocyanin, and azurin have established that the charge transfer interpretation is preferred (10, 11). Intense bands (c 2 X 103) that appear to be analogous to the 600-nm system of blue proteins are observed between 300 and 350 nm in the Co (II) derivatives. The shift in band position of about 16 kK [Cu(II) << Co (II)] accords well with expectation for an LMCT transition. The visible and near-infrared absorption, CD, and MCD spectra of Co (II) derivatives of stellacyanin, plastocyanin, and azurin have been interpreted (12) successfully in terms of the d-d transitions expected for distorted tetrahedral metal centers (Table I). Average ligand field parameters are the same for all three Co (II) proteins (Dq = 490, B = 730 cm"1), which strongly suggests that the donor atom... 

The spectrum for the 600°C-calcined fluorine-treated erionite sample shows substantial shifts in band positions, but band sharpening is less obvious. The bands at 1082, 792, 578, 470 and 438 cm- are shifted to 1098, 814, 585, 477 and 444 cm , respectively, after fluorine treatment and 600°c calcination. The large shifts observed are evidence of dealumination. The splitting of the 1082 cm-1 band into a doublet located at 1098 and 1085 cm-1 and some degree of band sharpening imply structure stabilization for fluorine treated erionite. 

The results indicate that both NH4,TMA-fl and NH.,K-L are de-aluminated upon fluorination. Strong supporting evidence comes from framework I. R. data where the shifts in band position to higher wave numbers are as much as 20 cm-1. However, there is no evidence of structure stabilization. Also McBain water adsorption data give no indication of surface hydrophobicity. Therefore, it is likely that structure defects are formed in these two zeolites as a result of dealumination and cause low thermal stability. 

These efforts were extended to the CI3 and Brs anions, as well as to the mixed trihalide anions. The reaction of alkali chloride salts with CI2 in argon gave rise to distinctive bands between 200 and 400 cm in both the infrared and Raman spectra (48). These have been assigned to CI3, which showed similar band positions in solution with bulky tetraalkylammonium cations (49). A shift in band position was observed with a change in cation. 

The variation in intensity and widths of the positive and negative peaks centred around 2060 cm-1 were interperted in terms of a potential-dependent shift in band position and energy of linearly adsorbed CsO at constant... 

The calibration curve is obtained by plotting the ratio of the absorbance of the analyte to that of the internal standard, against the concentration of the analyte. The absorbance of the internal standard varies linearly with the sample thickness and thus compensates, for it.. The discs or mulls must be made under exactly the same conditions in order to avoid any intensity changes or shifts in band positions. 

Slight temperature variations may lead to a shift in band positions and to changes in absorbance. This is of particular importance for quantitative evaluation of NIR spectra. The NIR spectra of water at several temperatures, shown in Fig. 

Simple solid mixtures may also be quantitatively analysed. These are more susceptible to errors because of the scattering of radiation. Such analyses are usually carried out with KBr discs or in mulls. The problem here is the difficulty in measuring the pathiength. However, this measurement becomes unnecessary when an internal standard is used. When using this approach, addition of a constant known amount of an internal standard is made to aU samples and calibration standards. The calibration curve is then obtained by plotting the ratio of the absorbance of the analyte to that of the internal standard, against the concentration of the analyte. The absorbance of the internal standard varies linearly with the sample thickness and thus compensates for this parameter. The discs or mulls must be prepared under exactly the same conditions to avoid intensity changes or shifts in band positions. 

Vasym(NO) bunds occurred on three different smectites (hectorite, SWy-1, and SAz-1), which indicated that the interaction is associated primarily with the hydrated cations and not directly with the smectite surface. In genml, the vibrational modes of the NO2 groups are relatively insensitive to interactions involving NO2 groups (74,75). In the context of prior vibrational studies of NACs, the shift in band positions of the v(NO) bands that were observed upon adsorption of TNB by smectite represent some of the largest shifts in vibrational studies of NACs that have been reported (74-81). 

DMB) environments. Shifts in band positions are plotted against concentration of 1,2-dimethoxybenzene sym/cycl Vjy (CO), cyclohexane environment sym/DMB V5y (CO), 1,2-dimethoxybenzene environment asym/cyd asytn( -0)- cyclohexane environment asym/DMB Vj,sy, (CO), 1,2-dimethoxy-benzene environment. 

This information has important implications in agricultural products. The water bands at 1450 and 1930 nm consist of multiple overlapping bands. The apparent location of these composite bands changes as the spectra are measured from one sample type to another. This apparent shift in band position is due to the changes in the relative proportions of the individual bands making up the composite bands. In addition, the concentrations of the molecular subspecies in any particular sample... 

Correction of scattering effects in cellular pixel spectra indicated by the binary mask. Resonant-Mie-induced scattering effects, discussed earlier, that can mix the real (dispersive) and imaginary (absorptive) line shapes of a vibrational transition, and thereby creating shifts in band position and intensity distortions in the observed spectra, are corrected by a phase-correction algorithm [28] between the real and imaginary components obtained by finite Hilbert transform (truncated reverse fast Fourier transform, FFT) [29]. 

Small shifts in band position may be observed for different cations. The various radii and charges of different cations alter the electrical environment of polyatomic anions and hence affect their vibrational frequencies. Obviously, different crystalline arrangements may result when the cation is altered. Normally, with increase in mass of the cation there is a shift to lower frequency. The characteristic bands of particular polyatomic ions are given in Table 22.1... 

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