Toward a three-dimensional treatment of channeling radiation

Abstract

Many authors have studied channeling radiation theoretically by means of the so called many beam approach. For axial channeling this approach tends to involve rather large eigenvalue problems if high accuracy is desired. With the extension to three-dimensional problems in mind we have therefore investigated the possibilities for a more efficient solution of these eigenvalue problems. The Lanczos algorithm [2] used in the preparation of Fig. 1 provides a substantial reduction of the numerical effort. We have also obtained some preliminary results for three-dimensional corrections to the tranverse problem. These corrections were found to be three-dimensional rather than longitudinal in character and tend to reduce the photon energy. The corrections are smaller than 1 percent for 4 MeV electrons in silicon. A more thorough investigation of these effects for the low energy part of the spectrum and a study of their impact on the high energy radiation [3] is now in progress. The conventional transverse many beam approach based on the Lindhard continuum approximation does not describe the latter effect.     

Molecular dynamics simulation of liquid tetrahydrofuran: on the uniqueness of force fields

Molecular dynamics simulations of liquid tetrahydrofuran have been performed with different force fields to illustrate that there is no unique way to model a given system of molecules. Parameters for the force fields have been taken from existing force fields and have been used as starting guesses for a simplex optimization. In spite of the very different final parameter values, all optimized force fields reproduce properly the physical properties for which they have been optimized, but not necessarily other ones.     

Spectroscopy and dynamics of the isolated sp2 CH chromophore in trideuteroacetaldehyde CD3CHO as derived from extrapolated SDCI ab initio calculations

Ab initio CI potential energy (PES) and dipole moment (DMS) surfaces have been calculated with singles and doubles excitation configuration interaction (SDCI) for the 2-dimensional isolated sp² CH chromophore subspace of trideuteroacetaldehyde (CD₃CHO). Different extrapolation schemes to full-CI have been applied after the extrapolation to full-SDCI. Vibrational band centres and absolute intensities are determined variationally on six extrapolated surfaces. The band centres are analysed within the effective Hamiltonian model for isolated CH chromophores and the effective spectroscopic parameters are compared for the different extrapolation schemes. Time dependent population evolution for vibrational quantum motion with a pure CH stretching state being initially populated is calculated for some of the extrapolated surfaces within the effective Hamiltonian model.     

Comparative structural analysis of 4,5- and 3,6-dialkylsulfanylphthalonitriles of different bulkiness

Phthalonitriles disubstituted by alkylsulfanyl moieties of different bulkiness (tert-butyl, adamantly, cyclohexyl and hexyl) and in 4,5- or 3,6-positions, respectively, set A and set B, have been prepared for comparative structural analyses. Miscellaneous parameters such as melting points and related polarity of the compounds are summarized. Substituents position and bulkiness effects on NMR and IR spectroscopy as well as refined X-ray structural data were examined.     

Dielectric interface effects in subsurface microscopy of integrated circuits

We investigate the defocus and image quality affected by a dielectric interface on high numerical aperture focusing of linearly polarized illumination in aplanatic mode. Theoretical and experimental demonstration is performed on subsurface backside microscopy of silicon integrated circuits, showing that the high longitudinal magnification provided by solid immersion lens microscopy allows the observation of significant astigmatism. It is shown that a 50 micron longitudinal displacement of the objective lens with respect to the sample is necessary to achieve maximum resolutions in two directions.     

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