The adsorption of CO on Pd(111) and Pd(100) have been studied using infrared reflection–absorption spectroscopy over a wide range of CO pressures and temperatures. A strong dependence of CO adsorption on the initial conditions was found for Pd(111) while CO adsorption on Pd(100) was essentially independent of the conditions of adsorption. Initial isosteric heats of adsorption of 30 and 38 kcal/mol were determined for Pd(111) and Pd(100), respectively. For Pd(111) and equilibrium phase diagram was constructed on the basis of the infrared (IR) data. The excellent correspondence among IR data for the single crystal Pd surfaces and a supported Pd catalyst suggests that the Pd particles in the supported catalyst consist primarily of low index [(111) and (100)] crystal faces.
Spatially resolved investigations of molecular properties in polymer materials sire shown to be possible by means of pareimeter-selective NMR imaging. The transformation of NMR psirameters into material properties can be performed using a suitable theoretical description of the molecular mobility in the polymer under investigation. Rubber ssunples consisting of three pieces of rubber with different crosslink densities have been investigated in a first experiment. A series of images which were progressively weighted by transverse relaxation have been acquired by application of a spin-echo back-projection technique. The relaxation was analyzed pixel by pixel using a single chain model for the molecular dynamics of the polymer network. Parameters directly related to material parameters, such as cross-link density and correlation times, could be derived from the theory and were displayed in the form of a MAterial Property image (MAP image). In contrast to conventional spin density images, where the different pieces of rubber could not be distinguished properly, the MAP image clearly reflects the different cross-link densities. Moreover, histogram analysis of the image can be used for the characterization of cross-link density inhomogeneities.
Electron paramagnetic resonance (EPR) has been used to investigate an acceptor in as-grown single crystals of ZnGeP2. The spectra are characterized by equally spaced triplets with 1:2:1 intensity ratios representing hyperfine interactions (varying from 35 to 55 G in magnitude) with two equivalent phosphorous nuclei. Their angular dependence shows that there are four crystallographically equivalent orientations of the defect. The principal values of the g matrix are 2.002, 2.021, and 2.074 and the corresponding principal axes, at one of the four sites, are the [011], [1̄00], and [01̄1] directions, respectively. Two possible models are suggested for this acceptor: Either a zinc vacancy (VZn) or a zinc ion on a germanium site (ZnGe). It also is suggested that the acceptor responsible for the EPR signal is the same acceptor, namely AL1, that gives rise to a dominant near-infrared absorption band.
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