Simplified non-empirical excited states calculations

The simple non-empirical method for calculating excited electronic states that we have presented recently has been applied on Rydberg states of ethylene. All kinds of ns, np and nd series have been studied using a Gaussian basis set including s, p and d functions. Calculated values of energy, oscillator strengths and other properties have been compared with the experimental spectrum. Assignments of all the observed series have been proposed.

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Zusammenfassung Die vor kurzem von den Verfassern entwickelte Methode zur Berechnung von angeregten elektronischen Zuständen wird auf Rydberg-Zustände angewendet. Alle ns-, np- und nd-Serien werden unter Benutzung eines Gaußschen Basissatzes mit s-, p- und d-Funktionen untersucht. Die errechneten Energiewerte, Oszillatorstärken und sonstigen Eigenschaften werden mit dem experimentellen Spektrum verglichen und den beobachteten Serien zugeordnet.

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We are indebted to Mrs. Janina Kowalewska for drawing the figures. One of us (J. K.) gratefully acknowledges support from Professor Ragnar Vestin.     

Monotonic convergent optimal control theory with strict limitations on the spectrum of optimized laser fields

We present a modified optimal control scheme based on the Krotov method, which allows for strict limitations on the spectrum of the optimized laser fields. A frequency constraint is introduced and derived mathematically correct, without losing monotonic convergence of the algorithm. The method guarantees a close link to learning loop control experiments and is demonstrated for the challenging control of nonresonant Raman transitions, which are used to implement a set of global quantum gates for molecular vibrational qubits.     

Polymer micelles from tadpole-shaped amphiphilic block-graft copolymers prepared by “Grafting-through” ATRP

A series of tadpole-shaped block-graft amphiphilic copolymers, i.e., block copolymers consisting of a cylindrical hydrophilic brush block and a coiled hydrophobic block were synthesized using “grafting-through” atom transfer radical polymerization. A tadpole-shaped block-graft copolymer from polystyrene bromide and a methacryloyl-terminated poly(tert-butyl acrylate) was prepared first. Then, hydrolysis of the poly(tert-butyl acrylate) side chains to polyacrylic acid side chains provided tadpole-shaped block-graft amphiphilic copolymers, which formed pH responsive micelles in water, the latter being confirmed by dynamic light scattering and atomic force microscopy.     

Nanostructure dependence of field-effect mobility in regioregular poly(3-hexylthiophene) thin film field effect transistors

Low polydispersity regioregular polythiophenes with number average molecular weights ranging from 2 to 13 kDa were cast under the same conditions from solution to form a series of field effect transistors (FETs). Tapping mode AFM and grazing incidence small-angle X-ray scattering revealed that in all cases the polymers formed regular nanofibrillar morphologies with the width of nanofibrils proportional to the weight average contour length of polymer chains, indicating that conjugated backbones were oriented perpendicular to the nanofibril axes. FET charge carrier mobilities exhibited exponential dependence on nanofibril width, pointing to the decisive role of extended conjugated pathways in charge transport.     

Nuclear-spin relaxation in nonrigid molecules: discrete multisite local dynamics combined with anisotropic molecular reorientation

Nuclear-spin relaxation is considered in a molecular system undergoing two types of dynamic processes: asymmetric-top small-step rotational diffusion and discrete multisite local jumps. The two processes are assumed to be uncorrelated. Time correlation functions for relevant rank-two interactions and corresponding spectral density functions are derived for a general relation between the characteristic rate constants. In addition, limiting cases of fast and slow local motions and of some specific jump conditions are also investigated.     

(1)H relaxation dispersion in solutions of nitroxide radicals: Effects of hyperfine interactions with (14)N and (15)N nuclei

(1)H relaxation dispersion of decalin and glycerol solutions of nitroxide radicals, 4-oxo-TEMPO-d(16)-(15)N and 4-oxo-TEMPO-d(16)-(14)N was measured in the frequency range of 10 kHz-20 MHz (for (1)H) using STELAR Field Cycling spectrometer. The purpose of the studies is to reveal how the spin dynamics of the free electron of the nitroxide radical affects the proton spin relaxation of the solvent molecules, depending on dynamical properties of the solvent. Combining the results for both solvents, the range of translational diffusion coefficients, 10(-9)-10(-11) m(2)∕s, was covered (these values refer to the relative diffusion of the solvent and solute molecules). The data were analyzed in terms of relaxation formulas including the isotropic part of the electron spin - nitrogen spin hyperfine coupling (for the case of (14)N and (15)N) and therefore valid for an arbitrary magnetic field. The influence of the hyperfine coupling on (1)H relaxation of solvent molecules depending on frequency and time-scale of the translational dynamics was discussed in detail. Special attention was given to the effect of isotope substitution ((14)N∕(15)N). In parallel, the influence of rotational dynamics on the inter-molecular (radical - solvent) electron spin - proton spin dipole-dipole coupling (which is the relaxation mechanism of solvent protons) was investigated. The rotational dynamics is of importance as the interacting spins are not placed in the molecular centers. It was demonstrated that the role of the isotropic hyperfine coupling increases for slower dynamics, but it is of importance already in the fast motion range (10(-9)m(2)∕s). The isotope effects is small, however clearly visible; the (1)H relaxation rate for the case of (15)N is larger (in the range of lower frequencies) than for (14)N. It was shown that when the diffusion coefficient decreases below 5 × 10(-11) m(2)∕s electron spin relaxation becomes of importance and its role becomes progressively more significant when the dynamics slows done. As far as the influence of the rotational dynamics is concerned, it was show that this process is of importance not only in the range of higher frequencies (like for diamagnetic solutions) but also at low and intermediate frequencies.     

Break junction tunnelling on Bi2Sr2CaCu2O8+δ-single crystals

Break junction tunnelling experiments on Bi₂Sr₂CaCu₂O₈₊-single crystals were performed at different temperatures. Carefully adjusted samples exhibited conductance curves showing only one large peak at positive and negative bias voltages. From these measurements a gap value =(21.2±2.8) meV, i.e. 2/k _B T _c =(5.5±0.8), was inferred. The behaviour of the conductance curves is similar to that of conventional superconductors but with a much larger broadening of the tunnelling characteristic. Therefore, several models which could explain this smearing are compared with the experimental data. However, it is found that none of them is capable of fitting the conductance curves convincingly. In some cases tunnel characteristics similar to those predicted by a charging effect model or a multigap model were obtained.This work was supported financially by the Deutsche Forschungsgemeinschaft through SFB 252.