Missing spots in low energy electron diffraction

Recent attempts to justify the use, after appropriate data averaging, of kinematical theory in surface structure determination by LEED, make it important to be able to distinguish truly kinematical features from those which can also be predicted from entirely general symmetry arguments. Such arguments are therefore developed formally into a set of rules determining the consequences of symmetry for LEED patterns. In particular the conditions for missing spots due to the presence of glide planes are given. It is pointed out that in some circumstances the isotropic scatterer model leads to spurious selection rules, that will not be satisfied in general.     

Determination of boron traces in rye grass BCR 281 by isotope dilution mass spectrometry

Summary A method for the isotope dilution mass spectrometric (IDMS) determination of boron in rye grass at the 5 g · g^–1 level has been developed. The mass spectrometric measurements are performed using negative thermal ionization at masses 42 (¹⁰B¹⁶O¹⁶O^–) and 43 (¹¹B¹⁶O¹⁶O^–). The ¹⁰B/¹¹B ratios are corrected for the ¹⁰B¹⁶O¹⁷O^– contribution at mass 43 and for mass fractionation. The chemical blank is determined using the standard addition method. The numerical calculations are done with a least square fit computer program. The method has been applied for the certification of boron in BCR 281 (Rye Grass). The boron content of this reference material has been established as (5.64±0.56) g·g^–1.

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Bestimmung von Borspuren in Rye Grass BCR 281 durch Isotopenverdünnungs-Massenspektrometrie

     

Nucleophilic displacement of aromatic fluorine. Part V. Use of nitrogen heterocycles as nucleophiles

The scope of the nucleophilic displacement of aromatic halogens on 1,4-benzodiazepine precursors by the anions of pyrroles, pyrazoles and imidazoles was studied both with and without electron-withdrawing substitutents on the heterocyclic nucleophiles. Some of the products proved to be useful intermediates for the synthesis of novel fused 1,4-benzodiazepines.     

Angular dependence of auger electron emission from Cu (111) and (100) surfaces

Experimental angular emission profiles of the M_2,3M_4,5M_4,562 eV Cu Auger electrons from clean copper (100) and (111) surfaces in several azimuths are presented. A simple single scattering theory to account for elastic scattering of the Auger electrons by other ion cores in the solid is presented, and calculations have been performed to assess the importance of this process in contributing to the observed angular dependence. These calculations produce angular structure having a similar magnitude and temperature dependence to that observed experimentally, and some featural similarity in peak positions or shapes. It appears that elastic scattering is an important source of angular dependence, and that studies of adsorbed species on surfaces should provide a very sensitive method of surface structure determination.     

Computer data analysis of the oscillating forward–reverse method

Nonequilibrium work theorems have recently gained wide acceptance as useful tools in determining free energy profiles for soft-matter systems. We have recently proposed an extension of the forward–reverse method, called the oscillating forward–reverse method; by introducing an oscillatory drift it enables the user to obtain PMFs from a single nonequilibrium pull. The analysis, although manageable, is non-trivial. We present here the data analysis and the software (OFR-AT) created to construct PMFs and associated uncertainties from the oscillating forward–reverse (OFR) method. The output analyzed by OFR-AT is often from molecular dynamics simulations, but as with the OFR method itself, it can be more generally applied. OFR-AT is a fast and efficient analysis tool that can analyze very large files (larger than 5 GB) in a short time period. We also describe the uncertainty and correlation calculations performed, provide a map of the data flow through the program, and present representative examples of PMF profiles calculated using OFR-AT.