Vibronic structure of the circular dichroism and absorption spectra of bianthryls

It will be shown that factors of virtually no influence on the vibronic structure of the absorption spectra in biaryls may profoundly change the correspoding vibronic structure in the CD spectra. This is illustrated by the theoretical analysis of the experimental vibronic absorption and CD spectra of some bianthryl derivatives.     

Another refinement of the right-hand side of the Hermite–Hadamard inequality for simplices

We establish a new refinement of the right-hand side of the Hermite–Hadamard inequality for convex functions of several variables defined on simplices.     

New Insight on Carbon Dioxide-Mediated Hydrogen Production**

A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7–8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO₂ under UV-C, the hydrogen production amounted to 0.6 μmol h⁻¹ during 24 h of radiation.     

Modeling of the dynamics of two coupled spherical pendula

We study the dynamics of the system of two spherical pendula mounted to the rigid beam which hang from the unmovable frame. Using Langrange’s multipliers the equations of motion have been derived. We identify two synchronous states in which pendula rotate in the same or different directions. The results of numerical simulations have been confirmed in the simple experiment.     

Laser frequency stabilization by magnetically assisted rotation spectroscopy

We present a method of Doppler-free laser frequency stabilization based on magnetically assisted rotation spectroscopy (MARS) which combines the Doppler-free velocity-selective optical pumping (VSOP) and magnetic rotation spectroscopy. The stabilization is demonstrated for the atomic rubidium transitions at 780 nm. The proposed method is largely independent of stray magnetic fields and does not require any modulation of the laser frequency. Moreover, the discussed method allows one to choose between locking the laser exactly to the line center, or with a magnetically-controlled shift to an arbitrary frequency detuned by up to several natural linewidths. This feature is useful in many situations, e.g. for laser cooling experiments. In addition to presenting the principle of the method, its theoretical background and peculiarities inherent to the repopulation VSOP are discussed.     

RAS: An efficient probe to characterize Si(0 0 1)-(2 × 1) surfaces

A complete inspection of the capabilities of reflectance anisotropy spectroscopy (RAS) in studying the adsorption of molecules or atoms on the Si(0 0 1)-(2 × 1) surface is presented. First, a direct comparison between RA spectra recorded on the clean Si(0 0 1)-(2 × 1) and the corresponding topography of the surface obtained using scanning tunneling microscopy (STM) allows us to quantify the mixing of the two domains that are present on the surface. Characteristic RA spectra recorded for oxygen, hydrogen, water, ethylene, benzene are compared to try to elucidate the origin of the optical structures. Quantitative and qualitative information can be obtained with RAS on the kinetics of adsorption, by monitoring the RA signal at a given energy versus the dose of adsorbate; two examples are presented: H₂/Si(0 0 1) and C₆H₆/Si(0 0 1). Very different behaviours in the adsorption processes are observed, making of this technique a versatile tool for further investigations of kinetics.     

Application of the TPR method for the studies of Ni(II) in Chrysoprase

TPR method was used to elucidate the status of nickel ions in chrysoprase. Temperature profiles of chrysoprase samples were interpreted by comparing them with TPR curves of references. Two kinds of nickel species were identified in the studied samples. The first one is nickel in 2:1 layer silicates while the other is nickel in the extra-framework positions. Apparent activation energies (85±3 and 20±5 kJ mol⁻¹) which were obtained from TPR data support the above attribution. This revised version was published online in July 2006 with corrections to the Cover Date.