Infrared absorption/desorption

Fig. 1. (a) A chemical structure of a 2.5th generation carboxylic acid-terminated poly(amido amine) (PAMAM) dendrimer. (b) Transmission surface enhanced infrared absorption spectra (SEIRAS) of dendrimer adlayers prepared at 30 min adsorption from aqueous solutions (0.01 wt.%) of a dendrimer at different pHs. Numerical values are pHs of the solutions, (c) Adsorption-desorption profiles as a function of time at different pHs and adlayer thicknesses at adsorption and desorption equilibrium as a function of pH for aqueous solutions (0.1 wt.%) of the dendrimer. The symbols, j and J, in the top figure denote start of adsorption and desorption, respectively. In the bottom figure, filled circle and opened square denote adlayer thicknesses at adsorption and desorption equilibrium, respectively. The dark tie denotes the calculated dendrimer size width. A solid curve is drawn to be visual, (d) Schematic illustration of dendrimers adsorbed at different pHs. Reprinted with permission from Ref. [69], 2006, American Scientific Publishers. 

This paper describes the further physical and chemical characterization of these two new forms of molecular carbon." Our results include the high-yield production (14%) of soluble material under optimized conditions, consisting of only C o and C70 in measurable quantity. These have been separated in analytical amounts by column chromatography and have been characterized in pure or mixed forms by a combination of electron impact, fast atom bombardment (FAB), and laser desorption mass spectrometry. Spectroscopic characterization is reported including the C NMR spectrum and the infrared absorption spectrum for the crude... 

As well as ammonia, adsorption and desorption of several other basic gas molecules, e. g. pyridine, are employed to measure the number and the strength of acid sites. Infrared absorption spectroscopy of adsorbed pyridine can indicate the nature of the acid sites (Brpnsted or Lewis acid). 

Although ATR has been used to quantify the variation in composition at the surface in TPEs (Sung and Hu, 1980), a related utility is its ability to monitor in situ processes such as reaction injection molding (RIM) (Ishida and Scott, 1986) and protein adsorption onto a polyurethane substrate (Pitt and Cooper, 1986). In the latter, the effect of shear rate on the kinetics of protein adsorption and desorption from phosphate-buffered saline (PBS) was studied in a specially designed flow cell. A very thin film of the commercial MDI-ED-PTMO polyurethane Biomer was cast from solution onto a Ge ATR prism. The thickness of the film was less than the penetration depth so the protein concentration could be monitored after the infrared absorption of the polymer... 

The characteristic infrared absorption of the sulphates is treated in Vol. IB, Chapter 4 and MS data in Vol. IB, Chapter 7. Recently, field desorption MS for carotenoid sulphates has been discussed [18]. It should be noted that molecular ions are not observed upon ordinary electron impact MS. NMR data are given in the original literature [2,5-7,11,14]. 

Figure 14 Surface-enhanced time-resolved IR reflection spectra monitoring the adsorption and desorption of fumaric acid on a gold electrode. (Reproduced with permission from Osawa M (2002) Surface-enhanced infrared absorption spectroscopy. In Chalmers JM and Griffiths PR (eds.) Handbook of Vibrational Spectroscopy, vol. 2, pp. 785-799. Chichester Wiley John Wiley Sons Ltd.)...

Studies to determine the nature of intermediate species have been made on a variety of transition metals, and especially on Pt, with emphasis on the Pt(lll) surface. Techniques such as TPD (temperature-programmed desorption), SIMS, NEXAFS (see Table VIII-1) and RAIRS (reflection absorption infrared spectroscopy) have been used, as well as all kinds of isotopic labeling (see Refs. 286 and 289). On Pt(III) the surface is covered with C2H3, ethylidyne, tightly bound to a three-fold hollow site, see Fig. XVIII-25, and Ref. 290. A current mechanism is that of the figure, in which ethylidyne acts as a kind of surface catalyst, allowing surface H atoms to add to a second, perhaps physically adsorbed layer of ethylene this is, in effect, a kind of Eley-Rideal mechanism. 

As will be shown later, the surface coverages of CO vary with distance into the pellet during CO adsorption and desorption, as a result of intrapellet diffusion resistances. However, the infrared beam monitors the entire pellet, and thus the resulting absorption band reflects the average surface concentration of CO across the pellet s depth. Therefore, for the purpose of direct comparison between theory and experiment, the integral-averaged CO coverage in the pellet... 

Figure 10.20 (A) Temperature-programmed desorption (TPD) and (B) Infrared reflection absorption spectroscopy (IRAS) spectra of CO adsorbed on Au/FeO(111) as a function of Au coverage. (Reprinted from Lemire, C. et al., Angew. Chem. Int. Ed., 43, 118-121,2004. With permission from Wiley-VCH.)...

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

The photochemical and thermal stabilities of Ru complexes have been investigated in detail [8,153-156]. For example, it has been reported that the NCS ligand of the N3 dye, cri-Ru(II)(dcbpy)2(NCS)2 (dcbpy = 2,2 -bipyridyl-4,4 -dicarboxylic acid), is oxidized to produce a cyano group (—CN) under irradiation in methanol solution. It was measured by both ultraviolet-visible (UV-vis) absorption spectroscopy and nuclear magnetic resonance (NMR) [8,153]. In addition, the intensity of the infrared (IR) absorption peak attributed to the NCS ligand starts to decrease at 135°C, and decarboxylation of N3 dyes occurs at temperatures above 180°C [155]. Desorption of the dye from the 2 surface has been observed at temperatures above 200°C. 

The term 1 or h indicates low or high coverage of adsorbed ethene, as inferred from ethene exposures.h TPD, temperature-programmed desorption LITD, laser-induced thermal desorption 1 FT-MS, Fourier-transform mass spectrometry SIMS, secondary-ion mass spectrometry MS, mass spectrometry T-NEXAFS, transient near-edge X-ray absorption fine structure spectroscopy RAIRS, reflection-absorption infrared spectroscopy. d Data for perdeut-erio species.1 Estimated value. 

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