Photoacoustic spectrum

The application of infrared photoacoustic spectroscopy to characterize silica and alumina samples is reported. High quality infrared photoacoustic spectra illuminate structural changes between different forms of silica and alumina, as well as permit adsorbate structure to be probed. Adsorption studies on aerosil suggest adsorbed species shield the electric fields due to particle-particle interactions and induce changes in the vibrational spectra of the adsorbates as well as in the bulk phonon band. It is shown that different forms of aluminum oxides and hydroxides could be distinguished by the infrared spectra. 

Transmission spectroscopy offers two significant advantages over photoacoustic spectroscopy of powders. First, transmission spectroscopy is not susceotible to external acoustic disturbances. Commercial spectrometers must be modified for vibrational isolation in order to obtain good photoacoustic spectra. Secondly, transmission spectroscopy can use solid state detectors with very fast response times, whereas photoacoustic spectroscopy is much slower, with spectra taking a few minutes to collect as compared to a few seconds for transmission spectra when both are taken with an FTIR. 

The infrared photoacoustic spectra presented here complement and extend previous results from transmission infrared studies. As an extension of previous studies of silica the photoacoustic results presented here have identified features in the infrared spectra that coincide with bulk phonon modes between 1000 and 1200 cm and below 500 cm . The photoacoustic spectra of water adsorbed on aerosil... 

A noteworthy feature of the photoacoustic spectra shown in Figure 2 Is the presence of water librations. These are frustrated rotations and have been observed for ice (24) by infrared spectroscopy, as well as for water adsorbed on Ft and Ag surfaces by electron energy loss spectroscopy (25-27). The three libration modes have been associated with the bands at 600, 538 and 468 cm" > this set of peaks occurs for water adsorbed on both the hydroxylated and methoxylated silica. 

Thus while one never sees commercial FT spectrometers for ultraviolet-visible (UV-VIS) absorption measurements (because photomultiplier tubes are much quieter detectors than are microphones), FT-VIS/PA spectrometers have been built that permit speedier acquisition of high S/N photoacoustic spectra (6-7). 

Light scattering by the sample can cause correctable (14) errors in photoacoustic spectra, particularly at visible amJ shorter wavelengths. However, at mid-infrared wavelengths this is no longer an Important consideration. 

Figure 6. Photoacoustic spectra of sulfided HDS catalysts. Frequencies (cm-1) of the most prominent absorbance bands of pyridine on the sulfided Mo/AloOj and Co-Mo/AlgOj are indicated. Only bands representative of Lewis acid sites are observed.

Photoacoustic spectra are recordings of the energy emitted as heat after absorption of monochromatic light. The sample is placed in a closed photoacoustic cell. The light beam, which is chopped at an audiofrequency, induces a periodic heating and cooling of the gas in contact with the sample in the cell. This is sensed as sound by a sensitive microphone. The... 

Figure 2.7 FTIR-photoacoustic spectra of pure CSM, b) N110 carbon black, c) CSM/...

The 1378 cm"1 band is from the CH3 symmetric bending and the 1156 cm 1 band is a complex skeletal vibration involving the CH3 branch of propylene. The 722 cm"1 band represents the CH2 rock and the 1462 cm"1 band is a combination of the CH2 scissor and the asymmetric CH3 bend. In the photoacoustic spectra the 1378 and 1462 bands are strong while the 1154 and 722 cm"1 bands are weak. Least squares linear regression... 

Figure 3.8 FTIR photoacoustic spectra of (a) net CSM, (b) carbon black N110, (c)...

The intensity changes of the N-H and C=0 bands are mostly responsible for the intermolecular forces between the polymer chains. Let us now determine how the polymer backbone is affected by the external stretching forces. In order to do so, tj e band due to the C-C aromatic stretchir g at 1408 cm" and the C-N in-plane bending at 1261 cm modes will be examined. Figure 4, traces A through F, depicts the rheo-photoacoustic spectra in the 1450-1200 cm" region. 

J. Wang et al., Near Infrared Photoacoustic Spectra of Model Homo-Polypeptides, J. SPIE, 2089, 492 (1996). 

Near-IR photoacoustic spectra have been reported for talc and other minerals [38]. Samples were passed through a 240-mesh (64jim) sieve, and were ground first if necessary. The powder was oven-dried overnight at 105°C prior to analysis. Bands were observed at 1.4S (O-H band), 2.14, 2.18, 2.27, 2.36, 2.43, and 2.S0 /tm. The UV-visible photoacoustic spectrum was featureless. 

Irradiation into this band caused photoisomerization, appreciable quantities of the 11-cw-isomer being formed. Several papers189-191 report calculations related to the spectroscopic properties of retinylidene Schiff bases. The principal absorption axes of rhodopsin and prelumirhodopsin have been determined.192 Photoacoustic Spectroscopy. The photoacoustic spectra of visual pigments have been reported.198... 

Photoacoustic spectra of resin samples have also been reported (16,17). The photoacoustic spectrum of TentaGel S beads coupled via a trityl linker with Fmoc-protected tryptophan is shown in Fig. 4. Compared with the photoacoustic spectrum of native aminoethyl TentaGel S beads, the appearance of diverse carbonyl bands is clearly seen the ester band of the linker at 1750 cm-1, the carbamate band of Fmoc protecting group at 1723 cm-1, and the amide I band at 1660 cm-1. 

Eu(tta)3L2] and [Eu(bta)3L2] have been determined by photoacoustic methods.Although glass transitions of the vitrified mesophase could not be detected by luminescence measurements, photoacoustic spectra clearly showed this transition. 

Fig. 26. Photoacoustic spectra of as-synthesized (left) and calcined CoAPO-44 at different modulation frequencies a 25, b 200 and c 1600 Hz. Reprinted from [63] with kind permission of Elsevier Science NL, Sara Burgerhartstraat 25,1055 KV Amsterdam, The Netherlands...

Fig. 14. Photoacoustic spectra of water in VIS and NIR regions normal absorption of HjO (upper spectra) and after compensation of H O against H2O (lower spectra) [19]...

Fig, 18. Photoacoustic spectra of Am III)in 10 M EDTA in different Am(III) concentrations [19] Table 1. The LPAS sensitivities of actinide ions determined in different solutions... 

Fig. 19. Photoacoustic spectra of Am(IIl)-hydro-lysis species with increasing pH [44]...

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