Normalized temperature and dissociation energy of diatomic molecules

The normalized temperatures known for spectral lines of atoms and ions can also be determined for band systems of diatomic molecules. Because of their dependence on at least five parameters, formulas of general applicability cannot be evaluated.Some similarities with the behaviour of atomic and ionic lines, however, can be found. The temperature range of maximum emissivity of a band system of diatomics is determined in first order by the dissociation energy of the corresponding molecule.Effects of dilution, the influence of pressure and interference problems in poly-component systems, as well as restrictions for the applicability of the normalized temperature concept, are discussed.     

Näherungslösung zur Ermittlung der Halbwertstemperatur zweiatomiger Gase

A simple calculation shows how the position of the specific heat maximum, caused by dissociation of diatomic molecules, depends on both the dissociation energy and on the internal partition sum of the molecules. The simplification that the internal sum over states of nearly all molecules can be treated as quadratic function with temperature leads to an equation generally applicable to diatomic molecules. The coefficients of this equation can be described by fundamental atomic and molecular constants. The dissociation range for different molecules is demonstrated by means of a graphic method.     

Zur Methodik der chemischen Vitamin A- und D-Bestimmung mit elektrophilen Metallhalogeniden

Ohne ZusammenfassungDer deutschen Forschungsgemeinschaft haben wir für die Unterstützung der Arbeit bestens zu danken.     

Ultrashort in-plane semiconductor microlasers with high-reflectivity microstructured mirrors

We present very compact, as short as 20 m long, low-threshold in-plane semiconductor lasers operating at a wavelength of 980 nm, in which microstructured mirrors have been formed at both cavity ends by deep reactive ion etching (RIE). The back mirror consists of a seven-period third order Bragg reflector with a measured reflectivity of 95%. The front mirror has a similar configuration, but consists of three periods with a lower reflectivity (80%) in order to allow output coupling. Lasing has been achieved from 20 m long and 8 m wide devices exhibiting a current threshold of 7 mA. These are among the shortest in-plane Fabry–Perot electrically pumped lasers demonstrated to date. Design issues are discussed, along with experimental data from which values for the reflectivity of the mirrors are derived. State-of-the-art electron beam lithography (EBL) and high-aspect-ratio RIE have been used for device fabrication, while additional strategies are proposed for the further improvement of the device performance.     

Ab initio structure of the active site of phosphotriesterase

This research exploits two recent developments to obtain a fundamental understanding of the metalloenzyme active site using the bimetallic enzyme phosphotriesterase as an example of this class. First is the theoretical prediction that the structure and spectroscopy of a native metalloenzyme active site is qualitatively determined by the supermolecule complex of the metal(s) and the first shell of ligands with proper charge states including waters directly bonded to ionic ligands. The second is the development of an effective potential for representing the molecular environment interacting with an all-electron active site in the quantum Hamiltonian. The GAMESS suite of electronic structure codes has implemented this new methodology, effective fragment potentials (EFP), to make theoretical calculations on structure, spectroscopy, and reactivity tractable for systems involving hundreds of atoms. Since there are transition metal cations at the active site of these enzymes, the all-electron part of the complex is calculated with relativistic compact effective potentials (CEP) and their concomitant basis sets. A realistic representation of the active site with its protein environment can be obtained using a combination of the CEP and EFP. This presentation will determine the inherent electronic and structural characteristics of phosphotriesterase using ab initio quantum mechanical methods. A single X-ray structure for the Zn-Zn enzyme is leveraged to obtain the structure of the Cd-Cd enzyme and to examine the consequences of protonating the active site.     

Experimental observation of evanescent modes at the interface to slow-light photonic crystal waveguides

We experimentally study the fields close to an interface between two photonic crystal waveguides that have different dispersion properties. After the transition from a waveguide in which the group velocity of light is v(g) ~ c/10 to a waveguide in which it is v(g) ~ c/100, we observe a gradual increase in the field intensity and the lateral spreading of the mode. We attribute this evolution to the existence of a weakly evanescent mode that exponentially decays away from the interface. We compare this to the situation where the transition between the waveguides only leads to a minor change in group velocity and show that, in that case, the evolution is absent. Furthermore, we apply novel numerical mode extraction techniques to confirm experimental results.