Pushing the Envelope

Direct electron density determination from SAXS data opens up new opportunities. The ability to model density at high resolution and the implicit direct estimation of solvent terms such as the hydration shell may enable high-resolution wide angle scattering data to be used to calculate density when combined with additional structural information. Other diffraction methods that do not measure three-dimensional intensities, such as fiber diffraction, may also be able to take advantage of iterative structure factor retrieval. While the ability to reconstruct electron density ab initio is a major breakthrough in the field of solution scattering, the potential of the technique has yet to be fully uncovered. Additional structural information from techniques such as crystallography, NMR, and electron microscopy and density modification procedures can now be integrated to perform advanced modeling of the electron density function at high resolution, pushing the boundaries of solution scattering further than ever before.

Micro-Raman study of nanodiamonds from Allende meteorite

We have studied the Raman spectroscopic signatures of nanodiamonds from the Allende meteorite in which some portions must be of presolar origin as indicated by the isotopic compositions of various trace elements. The spectra of the meteoritic nanodiamond show a narrow peak at 1326 cm−1 and a broad band at 1590 cm−1. Compared to the intensities of these peaks, the background fluorescence is relatively high. A significant frequency shift from 1332 to 1326 cm−1, peak broadening, and appearance of a new peak at 1590 cm−1 might be due to shock effects during formation of the diamond grains. Such changes may have several origins: an increase in bond length, a change in the electron density function or charge transfer, or a combination of these factors. However, Raman spectroscopy alone does not allow distinguishing between a shock origin of the nanodiamonds and formation by a CVD process as is favored by most workers.

Structure model and small-angle scattering cross sections of latent ion tracks in dielectric solids

Knowledge of the morphology of ion damage trails, `latent ion tracks', typically a few nanometres wide and 10–125 µm long, created along wakes of swift heavy ions in dielectric solids, is a prerequisite for advancement of track applications in nanotechnology. Modeling the tracks as depleted columnar structures with soft to hard boundaries and cylindrical symmetry, the derivation of theoretical track small-angle X-ray scattering cross sections is reported. These quantities enable the determination of track structure parameters, specifically the track electron density function and its radial dispersion, from empirical scattering intensities. The derived expressions can be readily adopted for analysis of small-angle neutron scattering data.

Electronic Nature of B-H-B Bridges and Their Manifestation in Vibrational Spectra of 11-Vertex nido-Carbaboranes

AIM analysis of electron density function based on the results of DFT B3LYP calculations was carried out for six 11-vertex nido-carbaboranes containing B-H-B bridges. The vibrational modes of B-H-B bridges were investigated experimentally and theoretically. The results obtained allowed some conclusions about the electronic structure of the species studied and the role of B-H-B bridges in the cage bonding pattern.