Catalytic trimerization of isocyanates by neutral pentacoordinated silicon hydrides

Pentacoordinated hydrosilanes react with excess of aryl isocyanates to give isocyanurates under mild and neutral conditions. The catalytic species are the initially formed N-silylformamides, which incorporate three equivalents of isocyanate, and then rearrange to N-silylformamide and isocyanurates.     

Gross Dissolution of Natural Rhombohedral-shaped Calcite in Glacial Acetic Acid

Gross dissolution of natural rhombohedral-shaped calcite crystals in different concentrations of glacial acetic (0.3 to 3.4 M) diluted by distilled water is studied. Activation energy of reaction between calcite crystal and acetic acid is calculated and found constant. The preexponential factor is not constant with different concentrations. Weight loss per unit surface area versus concentration of acetic acid is plotted at various temperatures (30 to 55 °C). It is found that the maximum weight loss per unit surface area occurs with 2.5 M of glacial acetic acid for the above temperature range. The value of the pre-exponential factor is also maximum at 2.5 M of acetic acid. The maximum weight loss per unit surface area is explained with the help of ionic conductivity and viscosity of the etchant.     

Excitation of Forbidden Electronic Transitions in Atoms by Hermite–Gaussian Modes

Photoexcitation of trapped ions by Hermite–Gaussian (HG) modes from guided beam structures is proposed and investigated theoretically. In particular, simple analytical expressions for the matrix elements of induced atomic transitions are derived that depend both on the parameters of HG beams and on the geometry of an experiment. By using these general expressions, the ${}^2{S}_{1/2}\to {}^2{F}_{7/2}$ electric octupole (E3) transition is investigated in an Yb⁺ ion, localized in the low–intensity center of the HG₁₀ and HG₀₁ beams. It is shown how the corresponding Rabi frequency can be enhanced by properly choosing the polarization of incident light and the orientation of an external magnetic field, which defines the quantization axis of a target ion. The calculations, performed for experimentally feasible beam parameters, indicate that the achieved Rabi frequencies can be comparable or even higher than those observed for the conventional Laguerre–Gaussian (LG) modes. Since HG-like modes can be relatively straightforwardly generated with high purity and stability from integrated photonics, these results suggest that they may form a novel tool for investigating highly-forbidden atomic transitions.     

Etch Pit Morphology on Calcite Cleavages by Glacial Acetic Acid

Etch pit morphology has been studied on calcite cleavages by different concentration of glacial acetic acid. Lateral reaction rates are very less at high concentration as well as low concentration of glacial acetic Acid. Etch pit morphology changes due to formation of finite or infinite lateral reaction rates at some particular concentration called transition concentration. The underlying chemical equations are given for different etch pit morphology.