Reflection spectra interpretation

Recently, the trimer theory has been used for the interpretation of the optical properties of the. Ymethylthiouronium salt [(MT)2(TCNQ)3 2H2Oj [67,68], The dominant feature of the polarized reflection spectrum cf (MT)2(TCNQ)3 2H20 (Fig. 13) is a broad intensive band of electronic reflection, with a sharp edge and low minimum at the frequency co = 9090 cm The intensive structure observed in the middle IR range (lines lto 8) is attributed to the e-mv coupling. Lines 2 and 4 have a fine structure which could be understood if one takes into account the equilibrium charge density shift pb = 0.25e and 3g = 0.15< in the two halves of TCNQ ( 3). 

As an illustration of the current state of the art for electronic spectroscopy of transition metal ions in zeolites, refer to the recent review by Schoonheydt of Cu2+ in different zeolites [56]. Schoonheydt shows that experimental measurement of diffuse reflectance spectra (and in the case of Cu2 + EPR spectra) must be combined with theoretical calculations if a complete interpretation is to be made. The exact frequencies of the d-d transitions in the electronic spectrum of Cu2+ are independent of the zeolite structure type, the Si Al ratio, and the co-exchanged cations, but depend solely on the local coordination environment. Figure 20 shows the diffuse reflectance spectrum of dehydrated Cu-chabazite the expanded portion reveals the three d-d transitions in the region around 15000 cm l. 

The total reflectance of an optically thick layer of dyed particles of AgBr can be measured with a spectrophotometer equipped with an integrating sphere. One then interprets the reflectance spectrum with the aid of Kubelka-Munk functions (20), as is commonly done with paints and pigments. 

Hi. Absorption spectra. The diffuse reflection spectrum of zirconium trichloride reported by Clark (108) shows an intense band at 17,300 cm with a shoulder at 21,000 cm which is interpreted as a ligand-... 

The modulation technique resolves the main technical difficulties of the constant potential spectral measurement at the electrode surface. Basically, in the modulation spectroscopic measurement, only the change associated with the change of the modulated parameter is detected. Thanks to lock-in ampHfication, we can significantly increase the sensitivity of the optical signal detection. It must be noted that what we can obtain is the change of the spectrum with respect to the modulated parameter but not the absolute reflection spectrum. In other words, modulation methods give the difference or differential spectrum. From the modulation spectrum, we cannot obtain explicitly the absolute spectrum at a unique condition unless a perfect reference absolute reflection spectrum is already in our hands. One should be careful in the interpretation of the spectral curves at this point. 

A reflection spectrum contains plenty of information about the stmcture of the interface and the state of the molecules at the interface. However, full understanding and interpretation of the spectrum is often difficult and has remained... 

In order to interpret the reflectance spectrum, modeling of the interface is the key issue. For example, in the simulation above, we tacitly made some assumptions. One is that the change of the optical properties of the substrate and refractive index of the solution immediately adjacent to the film surface are independent of potential and the presence of the film. The use of the Fresnel model with optical constants is based on the assumption that the phases in the three-strata model are two-dimen-sionally homogeneous continua. However, if the adsorbed molecule is a globular polymer which possesses a chromophore at its core, a better model of the adsorption layer would be a homogeneously distributed point dipole incorporated in a colorless medium. To gain closer access to the interpretation of the spectrum, a more precise and detailed model would be necessary. But this may increase the number of adjustable parameters and may demand a too complex optical treatment to calculate mathematically. Moreover, one has to pile up approximations, the validity of which cannot easily be confirmed experimentally. 

As a conclusion here, when the ER spectrum does not match with the difference absorption spectrum, the precise interpretation of the reflection spectrum... 

The color of a polymer sample is an observer s interpretation of the reflectance spectrum of the sample. While what we eall "color" is dependent on the observer, color is a critical property of polymers in commercial appUcations. Color is affected by the gloss or surface on a sample. Both the fraction of the fight reflected and the angle of reflection of that light are dependent on the surface roughttess of the sample. These two factors, in turn, affect how an observer perceives color. 

The influence of the oscillator strength on the spectrum of an adlayer on a metal measured by IRRAS can be interpreted in the following manner. Combining the Lorentzian oscillator model equation (1.46) for a single mode with the thin-fllm approximation equation (1.82) gives the reflectivity spectrum [100]... 

In addition, the GPC trace, an example of which is shown in Fig. 42, reflects the composition signature of a given product and reflects the spectrum of molecular chains that are present. Analysis of the area, height, and location of each peak provides valuable quantitative information that is used as input to a CUSUM analysis. Numeric input data from the GPC is mapped into high, normal, and low, based on variance from established normal operating experience. Both the sensor and GPC interpretations are accomplished by individual numeric-symbolic interpreters using limit checking for each individual measurement. 

The EPR spectrum is a reflection of the electronic structure of the paramagnet. The latter may be complicated (especially in low-symmetry biological systems), and the precise relation between the two may be very difficult to establish. As an intermediate level of interpretation, the concept of the spin Hamiltonian was developed, which will be dealt with later in Part 2 on theory. For the time being it suffices to know that in this approach the EPR spectrum is described by means of a small number of parameters, the spin-Hamiltonian parameters, such as g-values, A-values, and )-values. This approach has the advantage that spectral data can be easily tabulated, while a demanding interpretation of the parameters in terms of the electronic structure can be deferred to a later date, for example, by the time we have developed a sufficiently adequate theory to describe electronic structure. In the meantime we can use the spin-Hamiltonian parameters for less demanding, but not necessarily less relevant applications, for example, spin counting. We can also try to establish... 

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