Near infrared reflection spectrum

Near Infrared Reflectance Spectrum of a Nearly dried Sol Gel Body... 

In near-infrared reflectance, the matrix correction is made possible by the additivity of each weighted contribution for that wavelength in the spectrum being observed. The low absorptivity in the near-infrared contributes to this necessary "additivity" and eliminates, also, the necessity of sample dilution prior to sensing. 

The near-infrared reflectance provides the response to plasmon oscillations of the electron gas (which are uniform excitations). This region of the spectrum is, however, not sensitive to the strength of the short-range coulombic interactions, which prevent conductivity in a Mott-Hubbard insulating state. This is illustrated by the frequency-dependent conductivity cx((o) measured in various salts exhibiting very different values of the conductivity at room temperature (Fig. 27). The peak of the conductivity at the frequency w0 correlates with the metallic character namely, a low frequency of the peak position corresponds to a high dc conductivity and vice versa. The structures below 0)o are attributed to the coupling with intramolecular modes. 

Figure 1. Infrared reflectance spectrum of reduced YBa2Cu30y displaying onset of electronic absorption with a maximum near 640 cm.-l...

Near-infrared reflectance spectra for each sample were collected in triplicate by scanning through the base of the sample vials. Individual sample vials were inverted and rotated 120° between scans to ensure representative spectra. The triplicate scans were then averaged to obtain one spectrum for each bead sample. A variety of data preprocessing and calibration routines were evaluated in the development of quantitative regression models for determination of pellet potency and applied... 

The scope of the present chapter will be exclusively concerned with investigations of diffuse reflectance work performed in the UV/VIS region of the spectrum, and with colors that can be perceived by the human eye. Much work has been conducted in the near-infrared region of the spectrum, but that aspect will be covered elsewhere in this book. 

For n = 15 cereal samples from barley, maize, rye, triticale, and wheat, the nitrogen contents, y, have been determined by the Kjeldahl method values are between 0.92 and 2.15 mass% of dry sample. From the same samples near infrared (NIR) reflectance spectra have been measured in the range 1100 to 2298 nm in 2nm intervals each spectrum consists of 600 data points. NIR spectroscopy can be performed much easier and faster than wet-chemistry analyses therefore, a mathematical model that relates NIR data to the nitrogen content may be useful. Instead of the original absorbance data, the first derivative data have been used to derive a regression equation of the form... 

The thickness of thin film layers separated by uniform, parallel interfaces can be determined from optical interference patterns that result. These measurements can be made from about 400 nm out through the visible spectrum and on into the near-infrared (NIR) region. Since film thickness measurements rely not on the absolnte magnitude of the reflected light, but on the variation of that signal with wavelength, the choice of nnits is less important. Typically %R is used, but in some cases raw intensity is also satisfactory. We will treat thickness determinations in more detail in the applications section of this chapter. 

Fig. 8.20 a Differential absorption spectra (visible and near-infrared) obtained upon femtosecond flash photolysis (420 nm) of 8 in toluene with several time delays between 0 and 3000 ps at room temperature see color code for details. Arrows illustrate the changes, b Time-absorption profile of the spectra shown above at 457 nm (black spectrum) and 495 nm (red spectrum), reflecting the singlet excited-state decay and triplet excited-state formation, respectively... 

Figure 10.1 Comparisons of visible to near-infrared spectra of calcic pyroxene in transmitted and reflected light. Polarized absorption spectra of single crystals are correlated with the reflectance spectrum of a powdered sample of the same mineral (cf. fig. 5.14).

---