Comment on 'X-ray scattering from a randomly rough surface'

Recently, in this journal, Leskova and Maradudin published a new method for calculating x-ray scattering from a rough surface. In this comment their results will be compared with those obtained by other methods, especially the distorted-wave Born approximation. It is concluded that their results are useful in the limit of small transverse correlation length of the surface roughness. For intermediate values of the correlation length the results of both approximations are equivalent, being valid for small root-mean-square roughness and/or large incident perpendicular wavevector. In the case of large correlation length, neither approximation is correct. It is noted that the new method includes cross-polarization effects.     

High-resolution laser excitation spectroscopy of the A2E-X2A1 transition of SrCH3

High-resolution laser excitation spectroscopy has been used to record the A (2)E-X (2)A(1) electronic transition of SrCH(3) in a laser ablation/molecular jet source. Transitions arising from the K(')=1<--K(")=0, K(')=0<--K(")=1, and K(')=2<--K(")=1 subbands have been observed and assigned. The data were modeled with (2)E and (2)A(1) symmetric top Hamiltonian matrices in a Hund's case (a) basis, using a least squares fitting program. Rotational and fine structure parameters for the A (2)E state were determined. A comparison of the spin-orbit energy separation in the A (2)E state to other strontium containing free radicals showed that the Jahn-Teller effect is negligible. The spin-rotation constants for the A (2)E state were calculated using the pure precession model and were found to be in good agreement with the experimentally determined parameters. These calculations suggest that the A (2)E state of SrCH(3) is not entirely of p orbital character. The rotational constants were used to estimate the structural parameters of SrCH(3) in the A (2)E state. The strontium-carbon bond length was found to decrease by approximately 0.006 A, and the hydrogen-carbon-hydrogen bond angle opened by approximately 0.8 degrees compared to the X (2)A(1) state, similar to the geometry changes observed for CaCH(3).     

A simple catalytic method for the regioselective halogenation of arenes

This paper describes a mild palladium-catalyzed method for the regioselective chlorination, bromination, and iodination of arene C-H bonds using N-halosuccinimides as oxidants. These transformations have been applied to a wide array of substrates and can provide products that are complementary to those obtained via conventional electrophilic aromatic substitution reactions. [reaction: see text]     

Bulk electronic structure of metals resolved with scanning tunneling microscopy

We demonstrate that bulk band structure can have a strong influence in scanning tunneling microscopy measurements by resolving electronic interference patterns associated with scattering phenomena of bulk states at a metal surface and reconstructing the bulk band topology. Our data reveal that bulk information can be detected because states at the edge of the surface-projected bulk band have a predominant role on the scattering patterns. With the aid of density functional calculations, we associate this effect with an intrinsic increase in the projected density of states of edge states. This enhancement is characteristic of the three-dimensional bulk band curvature, a phenomenon analog to a van Hove singularity.     

A highly selective catalytic method for the oxidative functionalization of C-H bonds

This communication describes a new and highly practical Pd(II)-catalyzed method for the regio- and chemoselective oxidative functionalization of arenes and alkanes. Carbon-hydrogen bonds of substrates that contain a variety of directing groups (e.g., pyridine, azobenzene, pyrazole, and imine derivatives) are selectively transformed into esters, ethers, and aryl-halides under mild conditions. The scope of this reaction in terms of substrate, directing group, and oxidant is described, and a preliminary catalytic cycle is proposed.     

Intrinsic localized modes in microresonator arrays and their relationship to nonlinear vibration modes

Intrinsic Localized Modes (ILMs) are defined as localizations due to strong intrinsic nonlinearity within an array of perfect, periodically repeating oscillators. Such nonlinear phenomena have been studied for a number of years in the solid-state physics literature. Energy can become localized at a specific location in a discrete system as a result of the nonlinearity of the system and not due to any defects or impurities within the considered systems. Here, such mode localization is studied in the context of microcantilever arrays and microresonator arrays, and it is explored if an ILM can be realized as a forced nonlinear normal mode or nonlinear vibration mode. The method of multiple scales and methods to construct nonlinear normal modes are used to study nonlinear vibrations of microresonator arrays. Investigations reported in this article suggest that it is possible to realize an ILM as a forced nonlinear vibration mode. These results are believed to be important for future designs of microresonator arrays intended for signal processing, communication, and sensor applications.     

Spectrophotometric study of a hafnium-hematein chelate

A spectrophotometric study of an analytically useful hafnium chelate of hematein is presented. The stoichiometry, the formation constant, the optimal pH range and the free energy of formation of the chelate are described. Beer's law is obtained in the range 3–25 μg of hafnium(IV).The red-brown chelate, of probable formula HfO[hematein]₂, can be used for the colorimetric determination of hafnium in the presence of zirconium, if the molar concentrations of both metals are the same. The molar absorptivity of the hafnium chelate is 5.8·10⁴ 1 mole^-1 cm^-1 at 520 nm and pH 2.0 at room temperature.