Reflectance spectrum

The same that was said for UV-VIS absorption spectra is also valid for reflectance spectra, which are primarily used for quantitative estimation at constant wavelength and not for taking a scan over a broader wavelength range. The signals are low in energy and are not very characteristic. Nevertheless, or perhaps for this very reason, HODS is very successful and therefore particularly recommended. 

For practical work special optical devices are necessary. In this section we will cover the theory behind reflectance spectra and the use of these devices. 

If the surfaces are very smooth, for instance surfaces of high-polished metals, glass, crystals, and also liquids, the incident beam is not thrown back diffusely but is reflected in one direction of the same angle and in the same plane. Such a phenomenon is known as regular reflection, directed reflection, or specular reflection. The angle of the incident beam is - in relation to a perpendicular line - the same as that of the reflected beam, that is, = a,. (Fig. 4-50). 

Regular reflection and integral diffuse reflection should only be considered as ideal cases. In practice, the manner of reflection lies somewhere between these two extremes. Even on an excellent mirror, the reflection point is seen, and a heavily frosted surface has a certain direction of regular reflection. 

Diffuse reflection is a very complex process. Theoretically, it is assumed that reflected radiation is isotropic, which means that the radiation density is independent of the angle. If the size of the particles on the surface is of the same dimensions, as or is greater than the wavelength of the incident light d A), one can imagine that the radiation is both reflected on the surface in all directions and also regularly reflected, refracted, deflected, and partially absorbed inside the particles [31]. 

---

It is possible to identify particular spectral features in the modulated reflectivity spectra to band structure features. For example, in a direct band gap the joint density of states must resemble that of critical point. One of the first applications of the empirical pseudopotential method was to calculate reflectivity spectra for a given energy band. Differences between the calculated and measured reflectivity spectra could be assigned to errors in the energy band... 

Fig. 5. Reflection spectra of magenta dye developers (—) a xanthene (1) and (--) a metallized azo (Fig. 4b) compound. The lower blue absorption of the...

A solvent free, fast and environmentally friendly near infrared-based methodology was developed for the determination and quality control of 11 pesticides in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples inside glass vials and a multivariate calibration model to determine the active principle concentration in agrochemicals. The proposed PLS model was made using 11 known commercial and 22 doped samples (11 under and 11 over dosed) for calibration and 22 different formulations as the validation set. For Buprofezin, Chlorsulfuron, Cyromazine, Daminozide, Diuron and Iprodione determination, the information in the spectral range between 1618 and 2630 nm of the reflectance spectra was employed. On the other hand, for Bensulfuron, Fenoxycarb, Metalaxyl, Procymidone and Tricyclazole determination, the first order derivative spectra in the range between 1618 and 2630 nm was used. In both cases, a linear remove correction was applied. Mean accuracy errors between 0.5 and 3.1% were obtained for the validation set. 

Fig. 4.54. IR reflection spectra from an ODS monolayer on silicon for s- and p-polarized radiation at different incident angles ft Symmetric (s), asym-...

Fig. 23 Reflectance spectra (o—o—) of 3 pg testosterone (A) and 3 pg zT -androstendione-(3,17) (B) taken up on a silica gel layer compared with the absorption spectra determined m methanolic solution ( — —)...

The second method, based on measurements of IR reflection spectra, is simpler and enables working with larger volumes of molten salt. No special problems involving temperature and atmosphere control exist. The method was used successfully by Fordyce and Baum [336-338] in the investigation of fluoride melts containing tantalum and niobium. 

The main disadvantage of this method is that the IR reflection spectra must be recalculated and converted to absorption spectra, and possible distortion of the spectra by the thermal emission of the melt must be taken into account. 

Wilmshurst [353] observed the following bands were in the IR reflection spectra of some mixtures belonging to the LiF - NaF - KF - ZrF4 system (cm 1) 720, 520, 480, 240. The band at 480 cm 1 was assigned to bond vibrations of either ZrF5 or ZrF62, while bands at 520 and 240 cm 1 were... 

Artifact removal and/or linearization. A common form of artifact removal is baseline correction of a spectrum or chromatogram. Common linearizations are the conversion of spectral transmittance into spectral absorbance and the multiplicative scatter correction for diffuse reflectance spectra. We must be very careful when attempting to remove artifacts. If we do not remove them correctly, we can actually introduce other artifacts that are worse than the ones we are trying to remove. But, for every artifact that we can correctly remove from the data, we make available additional degrees-of-freedom that the model can use to fit the relationship between the concentrations and the absorbances. This translates into greater precision and robustness of the calibration. Thus, if we can do it properly, it is always better to remove an artifact than to rely on the calibration to fit it. Similar reasoning applies to data linearization. 

Other parameters which have been used to provide a measure of a include physical dimensions (thermomechanical analysis, TMA) [126], magnetic susceptibility [178,179], light emission [180,181], reflectance spectra (dynamic reflectance spectroscopy, DRS) [182] and dielectric properties (dynamic scanning dielectrometry, DSD) [183,184], For completeness, we may make passing reference here to the extreme instances of non-isothermal behaviour which occur during self-sustained burning (studied from responses [185] of a thermocouple within the reactant) and detonation. Such behaviour is, however, beyond the scope of the present review. 

Diverse series of diphenyl sulphoxide (DPSO) complexes of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(II) and Mg(II) with various large anions have been reported187-191. The complexes have the general formula M(DPSO)6(Anion) where M is the metal cation. The reflection spectra in the visible and near-IR region indicate an octahedral configuration around the metal ion surrounded by the DPSO molecules. Comparison with the spectra of DMSO complexes shows that they have almost identical structures. IR spectra indicate that the oxygen atom in the sulphinyl group is the donor atom in all these complexes. 

Very few studies on complexes of palladium and platinum with 1,1-dithiolato ligands have been reported recently. The electronic absorption spectra of the Et2dtc complexes of Pd and Pt, as well as Zn, Cu, Fe, Co, and Mn, have been measured in MeCN, EtOH, and -heptane, with diffuse-reflectance spectra also being determined (401). In 1969 and... 

The Sn Mossbauer data for Sn7S2Brio, Sn4SeBr, and Sn4TeBr, have been measured, and compared with those of the parent halides and chalcogenides. The data are consistent with a random distribution of halide and chalcogenide anions (104). Thus far, the reflection spectra of a few tin(IV) compounds assumed to be semiconductors have... 

The reflectance spectra of sohdified hquid sulfur previously equihbrated at temperatures of between 120 ° and 440 °C have been measured at 25 °C and color pictures of these sohdified melts were pubhshed [63]. These data were used to explain the yellow, orange and red colors of the sulfur flows on... 

The species S3 (absorbing at 420 nm) and S4 (absorbing at 530 nm) have been detected by reflection spectra in the condensate but the formation of S4 is unexplained [16]. S3 and SO2 have also been observed by Raman spectroscopy in such samples [15] (the expected S4 Raman line at 678 cm was probably obscured by the SS stretching mode of S2O at 673 cm but a shoulder at the high-frequency side of the S2O line indicates that some S4 may have been present). While the reddish colors turn yellow on warming at about -120 °C, the sulfur radicals could be observed by ESR spectroscopy up to 0 °C [10]. If the condensation of S2O gas is performed very slowly at -196 °C the condensate is almost colorless and turns red only if the temperature is allowed to increase slowly. Hence, it has been suspected that S2O is actually colorless like SO2. 

Fig. 1. UV-vis diffuse reflectance spectra of neat Ti02, chemically-modified and Ti02-loaded MCM-...

Lucovsky G, White RM, Benda JA, ReveUi JE (1973) Infrared-reflectance spectra of layered Group-IV and Group-VI transition-metal dichalcogenides. Phys Rev B 7 3859-3870 Cordes H, Schmid-Fetzer R (1994) Phase equilibria in the U-Te system. J AUoy Compd 216 197-206... 

Figure 1. Reflectance spectra of Fe-TsPc in 0.1 M NaOH adsorbed on the basal plane of a highly ordered pyrolytic graphite (HOPG) electrode at 0.90 V vs. a-Pd and on a Pt electrode at 0.70 V with Ar (0) and O2 ( A ) saturated solutions. Reproduced with...

Recently, the In situ Raman scattering from Fe-TsPc adsorbed onto the low Index crystallographic faces of Ag was examined and the results obtained are shown In Fig. 5 (15). On the basis of the similarities of these spectra with those obtained for the macrocycle In solution phase, as well as the polarization behavior characteristics, It has been concluded that the most likely configuration Is that with the macrocycle edge-on with respect to the surface. This Is In agreement with conclusions reached from the UV-vlslble reflectance spectra. The preferred configuration, however, may depend on the particular macrocycle, as well as on the nature of the adsorption site. 

These conclusions from the infrared reflectance spectra recorded with Pt and Pt-Ru bulk alloys were confirmed in electrocatalysis studies on small bimetallic particles dispersed on high surface area carbon powders.Concerning the structure of bimetallic Pt-Ru particles, in situ Extended X-Ray Absorption Fine Structure (EXAFS>XANES experiments showed that the particle is a true alloy. For practical application, it is very important to determine the optimum composition of the R-Ru alloys. Even if there are still some discrepancies, several recent studies have concluded that an optimum composition about 15 to 20 at.% in ruthenium gives the best results for the oxidation of methanol. This composition is different from that for the oxidation of dissolved CO (about 50 at.% Ru), confirming a different spatial distribution of the adsorbed species. 

UV diffuse reflectance spectra of the titanates were obtained with a JASCO UVIDEC-660 spectrophotometer using a sintered alumina disc as a reference. Raman spectra were recorded at room temperature on a JASCO NR-1100 spectrometer. 

Figure 4. UV diffuse reflectance spectra of BaTi409(-Ba4Tii303o(—) ...

---