Near-infrared

Continuous wave (CW) lasers such as Ar and He-Ne are employed in conmionplace Raman spectrometers. However laser sources for Raman spectroscopy now extend from the edge of the vacuum UV to the near infrared. Lasers serve as an energetic source which at the same hme can be highly monochromatic, thus effectively supplying the single excitation frequency, v. The beams have a small diameter which may be... 

Kneipp K, Kneipp H and Seifert F 1994 Near-infrared excitation profile study of surface-enhanced hyper-Raman scattering and surface-enhanced Raman scattering by means of tunable mode-locked... 

Shirakawa A, Sakane I and Kobayasi T 1998 Pulse-front-matched optical parametric amplification for sub-10 fs pulse generation tunable in the visible and near infrared Opt. Lett. 23 1292-4... 

Miller R E 1995 Near-Infrared laser optothermal techniques Laser Techniques in Chemistry 23, ed A B Myers and T R Rizzo (New York Wiley) pp 43-69... 

Kneipp K, Kneipp H, Deinum G, Itzkan I, Dasari R R and Feld M S 1998 Single-molecule detection of a cyanine dye in silver colloidal solution using near-infrared surface-enhanced Raman scattering App/. Spectrosc. 52 175-8... 

Jeiezko F, Tamarat P, Lounis B and Orrit M 1996 Dibenzoterryiene in naphthaiene a new crystaiiine system for singie moiecuie spectroscopy in the near infrared J. Chem. Phys. 100 13 892-4... 

Wang C, Mohney B K, Williams R, Hupp J T and Walker G C 1998 Solvent control of vibronic coupling upon intervalence charge transfer excitation of (NC)gFeCNRu(NH3)g- as revealed by resonance Raman and near-infrared absorption spectroscopies J. Am. Chem. Soc. 120 5848-9... 

Fast Fourier Transformation is widely used in many fields of science, among them chemoractrics. The Fast Fourier Transformation (FFT) algorithm transforms the data from the "wavelength" domain into the "frequency" domain. The method is almost compulsorily used in spectral analysis, e, g., when near-infrared spectroscopy data arc employed as independent variables. Next, the spectral model is built between the responses and the Fourier coefficients of the transformation, which substitute the original Y-matrix. 

Table 7.24 Absorption Frequencies of Other Double Bonds Table 7.25 Absorption Frequencies of Aromatic Bands Table 7.26 Absorption Frequencies of Miscellaneous Bands Table 7.27 Absorption Frequencies in the Near Infrared Table 7.28 Infrared Transmitting Materials...

TABLE 7.27 Absorption Frequencies in the Near Infrared Values in parentheses are molar absorptivity. 

Radio TV Microwave Millimetre wave Mid-infrared Near- infrared Visible Near- ultraviolet Far- ultraviolet X-ray Y-ray... 

For radiofrequency and microwave radiation there are detectors which can respond sufficiently quickly to the low frequencies (<100 GHz) involved and record the time domain specttum directly. For infrared, visible and ultraviolet radiation the frequencies involved are so high (>600 GHz) that this is no longer possible. Instead, an interferometer is used and the specttum is recorded in the length domain rather than the frequency domain. Because the technique has been used mostly in the far-, mid- and near-infrared regions of the spectmm the instmment used is usually called a Fourier transform infrared (FTIR) spectrometer although it can be modified to operate in the visible and ultraviolet regions. 

Mid- and near-infrared Nernst filament globar NaCl or KBr Grating interferometer Golay cell thermocouple bolometer pyroelectric photoconductive semiconductor... 

The attenuated total reflectance (ATR) technique is used commonly in the near-infrared for obtaining absorption spectra of thin Aims and opaque materials. The sample, of refractive index i, is placed in direct contact with a material which is transparent in the region of interest, such as thallium bromide/thallium iodide (known as KRS-5), silver chloride or germanium, of relatively high refractive index so that Then, as Figure 3.f8... 

Typical recording spectrophotometers for the near-infrared, mid-infrared, visible and near-ultraviolet regions... 

Figure 3.23 A typical double-beam recording mid-infrared and near-infrared spectrophotometer...

A diode, or semiconductor, laser operates in the near-infrared and into the visible region of the spectmm. Like the mby and Nd YAG lasers it is a solid state laser but the mechanism involved is quite different. 

The CO2 laser is a near-infrared gas laser capable of very high power and with an efficiency of about 20 per cent. CO2 has three normal modes of vibration Vj, the symmetric stretch, V2, the bending vibration, and V3, the antisymmetric stretch, with symmetry species (t+, ti , and (7+, and fundamental vibration wavenumbers of 1354, 673, and 2396 cm, respectively. Figure 9.16 shows some of the vibrational levels, the numbering of which is explained in footnote 4 of Chapter 4 (page 93), which are involved in the laser action. This occurs principally in the 3q22 transition, at about 10.6 pm, but may also be induced in the 3oli transition, at about 9.6 pm. 

There are many dyes available, each of which can be used over a 20-30 nm range and which, together, cover a wavelength range from about 365 nm in the ultraviolet to about 930 nm in the near-infrared. Dye concentrations are low, typically in the range 10 mol 1 to 10 mol 1. ... 

Observation, in the laboratory, of the a-X system of O2 represents a greater challenge because it is much weaker than the b-X system. It has been observed using CRDS, a 1.5 m cavity and O2 at atmospheric pressure. Because the transition is in the near infrared, mirror reflectivity is very high thereby increasing the sensitivity. 

Absorption and Fluorescence Spectra. The absorption spectra of actinide and lanthanide ions in aqueous solution and in crystalline form contain narrow bands in the visible, near-ultraviolet, and near-infrared regions of the spectmm (13,14,17,24). Much evidence indicates that these bands arise from electronic transitions within the and bf shells in which the Af and hf configurations are preserved in the upper and lower states for a particular ion. 

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

Characterization. In many cases, ftir is a timely and cost-effective method to identify and quantify certain functionaHties in a resin molecule. Based on developed correlations, ftir is routinely used as an efficient method for the analysis of resin aromaticity, olefinic content, and other key functional properties. Near infrared spectroscopy is also quickly becoming a useful tool for on-line process and property control. 

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