Spectroscopy FTIR PAS

An interesting extension of this type of reaction involves the photosubstitution of the surface-confined cobalt tetracarbonyl system [S] SiCo(CO)4 (where [S] represents a high surface-area silica) and the technique of Fourier transform infrared photoacoustic spectroscopy (FTIR/PAS) has been applied for the first time (172) to study photoreactions of a species on the surface. 

Fourier Transform Infrared (FTIR) and FTIR Photoacoustic Spectroscopy (FTIR-PAS) - Initial rates of polymerization, photoinitiator effects and oxygen effects were evaluated using these techniques. 

One of the major sample-handling problems in FTIR analysis of carbonaceous materials is that many of them are effective blackbody absorbers and thus are too opaque for direct transmission analysis in the midinfrared spectral region. Addition of KBr intensifies the signal to obtain transmission infrared spectra. It is time consuming, and grinding conditions and moisture are known to affect the spectrum of the sample [238]. Alternative techniques such as specular reflectance, diffuse reflectance (DRIFT), photoacustic spectroscopy (FTIR-PAS), and total... 

Recently, the preparation of two series of PTE of a new type with acid or ionic groups in the polyether SS and the investigation of their stucture-property relationships have been reported [49,65-69]. The first series was based on PTMG (M series) and the second on PEG (E series). The main interest was focused on understanding the influence of structure and morphology on the mechanisms of molecular mobility and ionic conductivity, as well as the relation between segmental mobility and ionic conductivity. For structural and morphological studies, DSC, WAXS, SAXS and Fourier transform infrared photoacoustic spectroscopy (FTIR PAS) were employed. The molecular dynamics and ionic conductivity were studied by DRS and TSDC. 

Photoacoustic infrared spectroscopy (FTIR PAS) was employed to characterize the different hydrogen bonds formed and to determine binding modes and chain orientation [69]. As an example, results of fitting analysis for the band in the C=0 stretching region are shown in Table 12 a sum of two bands, corresponding to free and hydrogen-bonded carbonyls, respectively, was fitted... 

The introduction of Fourier Transform Infrared Spectroscopy (FTIR) brought along a number of typical solid sample techniques. DRIFTS (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is probably most commonly known. Another technique, developed specifically for measuring solid, opaque samples is PAS (Photo Acoustic Spectroscopy). This accessory is less known, probably due to its high cost and its rather difficult modus operandi. 

Pesce-Rodriquez RA, Fifer RA. 1990. Photoacoustic FTIR investigation of a nitramine propellant system [Abstract], In 41st Pittsburgh Conference and Exposition on analytical chemistry and applied spectroscopy, Pittsburgh, PA, March 5-9, 1990. Aberdeen Proving Ground, MD U.S. Army Ballistic Research Laboratory, 5-9. 

FTIR photoacoustic spectroscopy (PAS) has advantages relative to conventional IR techniques (transmission, reflection and emission) because it is non-destructive, does not involve sample preparation and can probe samples with compositional gradients and layers. The theory, instrumentation, methods and applications of FTIR-PAS are discussed and results are presented on several polymer analyses based on FTIR-PAS. 4 refs. USA... 

Fourier Transform Infrared Spectroscopy (FTIR) provided a convenient tool by which reaction success was qualitatively evaluated. The spectrum of unfunctionalized PVBC on the polyethylene support is included in Figure 6a. Because of the intense absorbances of the PA, MPE, and IPE species, FTIR proved to be a convenient tool to investigate the progression of the syntheses. Note the changes in the spectra as the membranes were functionalized especially in the range of 900-1250 wavenumber for the MPE and IPE functional groups The PA functionalized membranes have several other very broad characteristic absorbances Figures 6b, 6c, and 6d contain the FTIR spectra of the membranes functionalized with the phosphorous species. Note that the intense absorbances around 3000 wavenumber are derived from the polyethylene support. 

Halttunen M, Tenhunen J, Saarinen T, and Stenius P (1999) Applicability of FTIR/PAS depth profiling for the smdy of coated papers. Vibrational Spectroscopy 19 261-269. 

Herres [182] has described a comparison of various spectroscopic methods (ATR-FTIR, PA-FTIR and LR-NMR) for the quantitation of plasticiser concentration in 0.2 mm thick PVC containing 9 wt.% Ti02 and 15-20 wt.% plasticiser. Sample sizes were in the range of g (LR-NMR), 100 mg (ATR-FTIR) and 5 mg (PA-FTIR). Quantitative analysis in normal transmission IR is limited for highly filled materials. For those cases the surface techniques ATR-FTIR and PA-FTIR may be applied. These FTIR methods yield information about migration and accumulation of low-MW species near the surface. ATR spectroscopy is well suited for quantitative analysis provided contact between the specimen and ATR crystal is reproducible. PA-FTIR samples some 8-15 /xm, Le. considerably more than the ATR technique (<2 /xm). The indirect detection method of PAS does not reach the sensitivity of normal FTIR measurements. Quantitative analysis of plasticisers in polymers by means of LR-NMR uses the fact that relaxation of protons in a magnetic field depends on the molecular environment. As shown in Table 6.38, LR-NMR is most precise and fast (0.5 min) in comparison to ATR-FTIR (2 min) and PA-FTIR (5 min). 

FT IK-PAS can also be used as a rapid and nondestructive technique for quantitative characterization of the surface degradation of aged polymers and other compounds. Using FTIR-PAS spectroscopy, oxidation profiles of the various photooxidized polyisoprene-polystyrene copolymers have been investigated. 

Spectroscopy, 490. See also 13C NMR spectroscopy FT Raman spectroscopy Fourier transform infrared (FTIR) spectrometry H NMR spectroscopy Infrared (IR) spectroscopy Nuclear magnetic resonance (NMR) spectroscopy Positron annihilation lifetime spectroscopy (PALS) Positron annihilation spectroscopy (PAS) Raman spectroscopy Small-angle x-ray spectroscopy (SAXS) Ultraviolet spectroscopy Wide-angle x-ray spectroscopy (WAXS)... 

In situ FTIR spectroscopy was used to study the adsorbed species generated on the catalyst surface in the presence of Hj and Oj. Before the experiment, the catalyst wafer was pretreated by O, (5.3 kPa) at 723 K for 1 h followed by evacuation at the same temperature in vacuum ca. 6x10 Pa) for 2 h. After the pretreatment, the temperature was decreased to a desired one in vacuum and IR spectrum was recorded at that temperature. The spectra of the catalyst wafer recorded at different temperatures were used as the background ones for the adsorption studies described below. 

The photoacoustic effect was first discovered by Alexander Graham Bell in the early 1880s [18], but it was not applied to Fourier transform infrared (FTIR) spectroscopy until a century later [19,20], Significant advantages of FTIR photoacoustic spectroscopy (PAS) include the following (1) Spectra may be... 

Fig. 5.12 The oxide thickness (broken line) and the free carrier absorption (dotted line, in arbitrary units) determined by FTIR spectroscopy for galvanostatic (top, 58 pA cm-2) and potentio-static (bottom, 7 V) conditions in buffered HF (0.1 M, pH=4.5). Redrawn from [Chi 2].

PAS spectra are similar to those obtained using ordinary Fourier transform infrared (FTIR) spectroscopy except truncation of strong absorption bands which occurs due to photoacoustic signal saturation. PAS allows the structure to be studied at different thicknesses because the slower the frequency of modulation, the deeper the penetration of IR radiation. 

IR Infra-Red Spectroscopy, including FTIR Fourier Transform IR PAS-IR IR Photo Acoustic Spectroscopy RS Raman Spectroscopy... 

A discussion of surface analysis requires a review of the depth being sampled during PA-FTIR spectroscopy. The depth being sampled during PA-FTIR analyses of rubbers is the thermal diffusion depth (Dt). This is a function of the thermal diffusivity of the sample, the wavenumber, and the mirror velocity. 

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