Integral band intensities

Figure 3.35 shows the potential dependence of the integrated band intensity of the linear CO observed in the experiment described above and the corresponding variation in the methanol oxidation current. The latter was monitored as a function of potential after the chemisorption of methanol under identical conditions to those employed in the IRRAS experiments. As can be seen from the figure the oxidation of the C=Oads layer starts at c. 0.5 V and the platinum surface is free from the CO by c. 0.65 V. The methanol oxidation current shows a corresponding variation with potential, increasingly sharply as soon as the CO is removed strong evidence in support of the hypothesis that the adsorbed CO layer established at 0.4 V acts as a catalytic poison for the electro-oxidation of methanol. 

Figure 3.35 Potential dependence or the ft) integrated band intensity of the linear COad< derived from methanol at 0,4 V vs. RHE in I M CH3OH/0.5M H SO and (2) the methanol electro-oxidation current observed after the adsorption of methanol at 0.4 V. From K. Kunimatsu, Berichte der Bunsen-Ceseiischaft jur Phy-sitcafische Chemie. 1900.94. 1025 1030-...

Figure 5. The integrated band intensity (1) and the band position (2) of linearly adsorbed CO are plotted as a function of potential in (a) 1 M HC104, (b) 1 M H2S04, and (c) 1 M HCL (Reprinted from ret 31. Copyright 1985 American Chemical Society.)...

Figure 6. The potential dependence of (1) the IR band center and (2) the integrated band intensity of adsorbed CN- on Au, and (3) the integrated band intensity of the [Ai CNy complex. (Reprinted from ret 25. Copyright 1988 American Chemical Society.)...

In forming intermolecular H-bonds the intensity alteration depends upon the -electron interaction energy share, With large energy. shares of the -electron interaction the integral band intensity remains either almost equal to that of a free group (a-oxyderivative of... 

For bands, the expression for the integrated band intensity is identical but with the integration over the whole band. 

The temperature dependence PiJ) of the integrated band intensities a T) at constant pressure can be expressed as... 

Nevertheless, the integrated band intensities of overtones and combination bands show a characteristic temperature dependence. As a result of the anharmonicity of the vibrations, these bands are observed in vibrational spectra. For overtones (At = n,n > I), the band intensity function of the temperature is expressed as... 

The validity of Eq. (7) was checked by comparing the calculated dipole moments of CO adsorbed on Cu and Pt with the corresponding values from inelastic electron scattering and from IR spectra in the gas phase [23]. For this purpose, Eq. (7) was written in the form of the integrated band intensity ... 

This is the mathematical expression for the integrated band intensity obtained from an IR reflection-absorption experiment. 

Fig. 10. Typical spectral features for solution species, (a) Band for the asymmetric Cl-O vibration of Ci04 ions, measured with s-polarized light. Spectra calculated as the ratio between the smgle-beam spectrum at the sample potential (as indicated) and a spectrum at 0.05 V. (b) Integrated band intensity for the Cl-O stretching of perchlorate ions in solution as a function of potential.

Figure 10 a and b shows the effect of applying an increasing positive potential to a plantinum electrode in HCIO4 solution. The integrated band intensities were taken from spectra measured with s-polarized radiation. The intensity of the band at 1100 cm , which is due to the asymmetric mode of CIO4 ions in the solution, follows the changes in H" concentration in the thin layer. 

Fig. 11. (a) Spectral features for sulfate species in solution, measured with s-polarized light at the indicated potentials reference spectrum taken at 0.05 V vs. RHE. Loss band at 1120cm asymmetric S-O stretch of SO4" gain band at 1190cm asymmetric stretch of HSO. Solution 0.5 M K2SO4+O.OI M H2SO4. (b) Integrated band intensities as a function of potential. 

Fig. 13. (a) Reflectance spectra for adsorbed hydrogen on polycrystalline Pt in 1 M H2SO4 at different potentials as indicated. Reference potential 442 mV (RHE). (b) Comparison of the linear sweep voltammogram at 0.1 V s on the negative scan over the hydrogen adsorption region with the integrated band intensity for the 2090 cm absorption band shown in (a). (After [43]). Reprinted by permission of Elsevier Science. 

The integrated band intensity for adsorbed sulfate ions on polycrystalline platinum shows a nonlinear dependence on the applied static electric field [165]. To account for this kind of behavior, an expression was derived [173] based on the fact that the integrated intensity is proportional to the transition moment (see Sec. 3.1) [23,174] ... 

A plot of the integrated band intensities for the 1200cm mode of sulfate adsorbed on Pt according to Eq. (25) is given in Fig. 62. From the slopes and the extrap-... 

Fig. 62. Square root of the integrated band intensity for the 1200 cm mode of adsorbed sulfate ions as a function of the applied electric field for A, 7, = 2 A, /, = 3 O, 7 = 4 , 7, = 5. 7, is the intensity of the solution loss band of sulfate obtained with s-polarized light and is proportional to the degree of coverage with surface ions [165].

Shindo, Fr. Benilan, Y. Chaquin, P. Guillemin, J.C. Jolly, A. Raulin, Fr. IR spectrum of C8H2 Integrated band intensities and some observational implications. J. Mol. Spectrosc. 2001, 210, 191-195. 

This is, of necessity, the case since EMIRS is a difference technique and, as such, does not allow any quantitative investigation into the adsorption process, i.e. it is not possible to compare any integrated band intensities since the separate "absolute spectra of the species present at the two potentials cannot be obtained. Nonetheless, the paper clearly does show the versatility of the technique in giving an insight into an electrochemical system, aided by the high degree of energetic control afforded by potential modulation. 

Fig. 29. (a) Potential dependence of the integrated band intensity A and (b) the wavenumber for the maximum absorption vT for the linearly adsorbed CO on a platinum electrode in 5M CH3OH + 1M HC104. 

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