Ab initio molecular dynamics simulations of a binary system of ionic liquids

This work presents first insights into the structural properties of a binary mixture of ionic liquids from the perspective of ab initio molecular dynamics simulations. Simulations were carried out for a one-to-one mixture of 1-ethyl-3-methyl-imidazolium thiocyanate and 1-ethyl-3-methyl-imidazolium chloride and compared to pure 1-ethyl-3-methyl-imidazolium thiocyanate.     

MOVPE homoepitaxy of high-quality GaN: Crystal growth and devices

Epitaxial growth on GaN bulk single crystal substrates sets new standards in GaN material quality. The outstanding properties provide insights into fundamental material parameters (e.g. lattice constants, exciton binding energies, etc.) with a precision not obtainable from heteroepitaxial growth on sapphire or SiC. With metalorganic vapor phase epitaxy (MOVPE) we realized unstrained GaN layers with dislocation densities about six orders of magnitude lower than in heteroepitaxy. By the use of dry etching techniques for surface preparation, an important improvement of crystal quality is achieved. Those layers reveal an exceptional optical quality as determined by a reduction of the low-temperature photoluminescence (PL) linewidth from 5 meV to 0.1 meV and a reduced X-ray diffraction (XRD) rocking curve width from 400 to 20 arcsec. As a consequence of the narrow PL linewidths, new features as, e. g. a fivefold fine structure of the donor-bound exciton line at 3.471 eV was detected. Additionally, all three free excitons as well as their excited states are visible in PL at 2 K.

Dry etching techniques for surface preparation allow morphologies of the layers suitable for device applications. We report on InGaN/GaN multi-quantum-well (MQW)_ structures as well as GaN pn- and InGaN/GaN double heterostructure light emitting diodes (LEDs) on GaN bulk single crystal substrates. Those LEDs are twice as bright as their counterparts grown on sapphire. In addition they reveal an improved high power characteristics, which is attributed to an enhanced crystal quality and an increased p-doping.     

Decay studies of neutron-rich products from 76Ge induced multinucleon transfer reactions including the new isotopes 62Mn, 63Fe and 71, 72, 73Cu

By irradiating a ^natW target with 9 MeV/u ⁷⁶Ge ions, neutron-rich isotopes in the chromiumgermanium region were produced. On-line mass-separated samples were investigated. The new isotopes ⁶²Mn, ⁷¹Cu, ⁷²Cu and ⁷³Cu were identified and their half-lives measured to be 0.88(15), 19.5(16), 6.6(1) and 3.9(3) s, respectively. The half-life of ⁶³Fe, a nucleus which has previously been detected using particle-identification techniques, was measured to be 4.9(5) s. Decay schemes were derived in most cases. Additional spectroscopic information was obtained on the decays of ⁷³Zn and ⁷⁴Zn. We give evidence that the earlier reported γ-ray activity attributed to ⁶⁷Ni belongs to the decay of the ⁷⁰Cu isomers. At A = 67 we observed a new β-ray activity of 21(1) s half-life which is here assigned to the decay of ⁶⁷Ni.     

Application of molecular orbital theory to the interpretation of mass spectra study of substituent effect on a series of acetophenones

Semi-empirical molecular orbital calculations have been used to study the substituent effect on the intensity of the m/e 43 peak ([COCH₃]+) in the mass spectra of a series of 25 substituted acetophenones. The two most relevant molecular properties calculated appear to be the ionization potential and the bond density of the fragmenting bond. A semi-logarithmic plot of relative peak intensities[the ratio of m/e (43/[M]⁺)] versus the ratio of ionization potential to bond density for these compounds produced a linear relationship with a correlation coefficient of 0.90 from the INDO method and 0.93 from the IEHT method. The use of two different semi-empirical methods to calculate ionization potentials and bond densities, together with the qualitative agreement between the two methods and with available experimental data, substantiates the correlations obtained. In addition, the molecular orbital calculations were used to understand the anomalous behavior of the teritary butyl and para-phenyl substitutes.     

Understanding the template preorganization step of an artificial arginine receptor

A biomimetic complex which mimics the arginine-phosphonate diester interaction of the arginine fork is investigated with respect to structure and energetics of stable configurations. Within this work, we provide knowledge on local minima of the isolated system obtained from first-principles calculations. Non-negligible solvation effects are studied in a microsolvation approach. The interactions which govern the structural patterns of molecular recognition in this tweezer-guest complex can be significantly modulated by the action of hydrogen bond accepting and donating solvent molecules, such as dimethyl sulfoxide or water, which were present in experimental investigations on this system. Different tweezer-guest structures are evaluated with respect to their temperature-dependent thermodynamical properties as products of the first association reaction step of the bisphosphonate tweezer template and the guanidinium moiety.     

Alpha decay of neutron-deficient isotopes with 78 ⪕ Z ⩽ 83 including the new isotopes 183, 184Pb and 188Bi

Using on-line mass separation of evaporation residues from heavy-ion-induced fusion reactions, three new isotopes were identified by their alpha decay, E_α given in keV: ¹⁸³Pb, 6715(20), ¹⁸⁴Pb, 6632(10) and ¹⁸⁸Bi, 6820(20). Half-lives were determined for ¹⁸⁴Pb, 0.55(6)s, ¹⁸⁵Pb, 4.1(3)s and ¹⁸³Tl, 0.060(15) s. The alpha branching ratios were re-measured for ^182–184Hg and ^{178, 179}Pt, the results are discussed within the framework of alpha width systematics.