Spectra, surface

At the time of writing, in all papers published on adsorption studies on oxides surfaces, spectra have been reported of samples held at the ambient temperature of the sample compartment. It is obvious that when dealing with very volatile adsorbates, low temperature sample cells may be required to increase adsorption and also to prevent rapid desorption of the adsorbed species. In some instances, it is also desirable to record the spectra of species held at elevated temperatures for better correlation with industrial catalytic systems. It should be noted that there are only a few infrared spectra reported in the literature for high temperature studies of catalytic reactions. Sample emission at elevated temperature is a significant experimental complication in investigations of this type. 

Figure 4. Carbon K-edge NEXAFS spectra of ethylldyne (a) and ethylene (b) adsorbed on the Pt(lll) surface. Spectra for two incidence angles (20 and 90 ) of the X-ray beam are shown.

Figure 71 compares the 2,000-1,000 cm-1 FTIR spectral region for the heat seal layers of the "good" and "bad" films, and the center opaque polyethylene layer for the "bad" film. Of particular interest is the carbonyl region between approximately 1,800 and 1,650 cm-1. The two heat seal surface spectra show mainly the vinyl acetate ester carbonyl band at 1,740 cm-1. For the middle polyethylene layer of the "bad" film, the shape and position of the carbonyl band is consistent with oxidative degradation of polyethylene. The peak maximum at... 

J. C. Vickerman and D. Briggs (eds.), TOF-SIMS Surface Analysis by Mass Spectrometry. Huddersfield, UK, IM Publications and Surface Spectra Limited, 2001. 

In surface-enhanced Raman spectroscopy (SERS) samples are adsorbed onto microscopically roughened metal surfaces. Spectra are the intensities and frequencies of scattered radiation originating from a sample that has been irradiated with a monochromatic source such as a laser. SERS spectra are of molecules that are less than 50 A from the surface. 

Similarities in the spectra of -heptane and the catalyst adsorbate suggest that -heptane is the dominant species on the H-ZSM-5 surface. Small peaks on the catalyst surface spectra indicate the presence of coke formation. " ... 

Hamilton, V. E., Wyatt, M. B., McSween, H. Y. and Christensen, P. R. (2001) Analysis of terrestrial and Martian volcanic compositions using thermal emission spectroscopy 2. Application to Martian surface spectra from the Mars Global Surveyor thermal emission spectrometer. Journal of Geophysical Research, 106, 14,733-14,746. 

C.) at concentrations below 5 X 10"5M. The p-toluenesulfonate (pts) salt of this cyanine was also used it gave identical surface spectra and adsorption data in silver and silver halide dispersions (23). Astra-phloxin (55) (l,l -diethyl-3,3,3, 3 -tetramethylindocarbocyanine pts,... 

Figure 8A. Adsorption isotherms of Pseudocyanine (No. 1, Circles) and of Astraphloxin (No. 2, Squares) in AgBr (Dispersion D) containing 0.2% gelatin at 23°C., pBr 3, pH 6.5. The data are expressed as the concentration of free dye (c) in equilibrium with dye adsorbed per mole of AgBr (a). Open data points and solid lines Results calculated from surface spectra. Solid data points and dashed lines Results obtained from phase-separation procedure B. Adsorption isotherms of Figure 8A expressed in terms of the Langmuir equation. See text...

C. Adsorption isotherms oj the thiacarbocyanine in the octahedral AgBr dispersion. Open data points Results calculated from surface spectra of Parts A and B. Solid data points Results obtained from... 

It remains to be determined to what extent the dye adsorption technique is applicable to other substrates. No evidence was obtained for Pseudocyanine adsorption to Mn02, Fe2Os or to pure silver surfaces, although this dye can be bound to mica, lead halides, and mercury salts with formation of a /-band (61). Not only cyanines but other dye classes can yield surface spectra which may be similarly analyzed. This is specifically the case with the phthalein and azine dyes which were recommended by Fajans and by Kolthoff as adsorption indicators in potentio-metric titrations (15, 30). The techniques described are also convenient for determining rates and heats of adsorption and surface concentrations of dyes they have already found application in studies of luminescence (18) and electrophoresis (68) of silver halides as a function of dye coverage. 

The spectra of the adsorbed butenes, pentenes, and hexenes discussed above were obtained by chemisorbing on a hydrogen-covered surface at 35° C. The results show that some dehydrogenation must occur under these conditions, since it is impossible to get four-point adsorption without having some dissociation. When higher-molecular-weight olefins (or paraffins) are chemisorbed on a bare nickel surface, spectra similar to A of Fig. 3 are obtained, and no distinguishing characteristics are observed. 

Figure 38 illustrates accumulated surface scans in the rhodium 3d and phosphorus 2p region taken from granules of the rhodium anchored catalyst. The surface concentration is low enough that scan accumulation was necessary to detect these elements. These particles were oxygen plasma etched for thirty minutes and Figure 39 includes a survey spectrum as well as Rh 3d and P 2p spectra taken from the sample after OPE. The intensity of the rhodium and phosphorus lines is enhanced considerably as a result of etching. To investigate the depth of penetration of the anchored metal into the surface of the particles, surface spectra were obtained as a function of OPE times. This data is given in Table VIII and the phosphorus and rhodium spectra as a function of etch time in minutes is shown in Figure 40. The intensity of the rhodium and phosphorus lines increases up to twenty minutes of etching or equivalent to penetration of 160 nm into the surface of the particles. This analysis indicates that rhodium is fairly uniformly distributed into the particles at least 160 nm into the interior.

Vickerman, J. C., Briggs, D., and Henderson, A., The Static SIMS Library, Surface Spectra (1997). 

Several national and international consensus standards organizations, such as the American Society for Testing and Materials (ASTM) and the International Standards Organization (ISO) have adopted a reference standard extraterrestrial spectral distri bution (ASTM E490 00a), and terrestrial reference spectral distributions for direct beam and total hemispherical (on a 37° tilted south facing surface) spectra at a pre scribed air mass of 1.5 (ASTM G173 03).2,1011... 

An advantage of PM-IRAS over SFG is that PM-IRAS provides IR surface spectra (p-s) and gas-phase spectra (s) in parallel. Thus, the catalytic turnover can be followed not only by gas chromatography, but also by PM-IRAS (cf. Figs 45 and 53). The efficiency of PM-IRAS has been demonstrated both with dispersed and Fourier-transformed IR spectrometers in the characterization of various metal surfaces (114,164-177). 

Figure 13.8. Raman spectra of R6G adsorbed from a methanol solution onto glassy carbon (B). The fluorescence normally encountered with 514.5 nm excitation is quenched upon adsorption to the conducting surface. Spectra of (A) solid R6G and (C) clean glassy carbon are shown for comparison. (Adapted from References 10 and 25 with permission.)...

Figure 7.6 Non-monochromatic X-ray radiation from an X-ray gun with an A1 target. The characteristic Alkaline is at about 1.5 keV. (Reproduced with permission from D. Briggs and J.T. Grant, Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications and Surface Spectra Ltd, Chichester. 2003 IM Publications.)...

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