AFM single molecule experiments at the solid-liquid interface: in situ conformation of adsorbed flexible polyelectrolyte chains

This paper reports the in situ study of conformations of flexible synthetic polymer molecules of protonated poly(2-vinylpyridine) at the solid-liquid interface at different pH of aqueous solutions. The direct conformation study of such thin ( approximately 0.4 nm) single molecules under liquid is performed for the first time. The highly protonated poly(2-vinylpyridine) chains possess a conformation of 2D equilibrated random coil, while at low degree of protonation, molecules are in the conformation of a strongly compressed 3D coil. Molecules are immobile during the few hours of the AFM experiment.     

Magnetic resonance in systems with equivalent spin-1/2 nuclides. Part 1

Electron paramagnetic resonance (EPR) spectra of S=1/2 systems XL(n) with n equivalent nuclei having spin I=1/2 have been simulated for microwave frequencies in the L-, X-, and W-bands. It has been shown that for n>2 nuclei, the EPR spectra have a more complicated form than anticipated from the usual oversimplified analysis, which predicts n+1 lines with intensity ratios given by the coefficients of the binomial expansion. For the XL(n) system with n=3, the EPR spectra in fact consist of six lines. The exact solution of the spin-hamiltonian for this case has been obtained, which gives four levels in zero magnetic field. For n>2 systems, the degeneracy of the energy levels cannot be completely removed by the Zeeman electronic and nuclear interactions. For n>4, certain spin states cannot occur, consistent with the (generalized) Pauli exclusion principle. Discussion of the underlying theory, invoking exchange degeneracy and the appropriate permutation group theory, is included in some detail. Analogous considerations hold for NMR spectroscopy of non-radicals.     

Discrete surface solitons

It is theoretically shown that discrete nonlinear surface waves are possible in waveguide lattices. These self-trapped states are located at the edge of the array and can exist only above a certain power threshold. The excitation characteristics and stability properties of these surface waves are systematically investigated.     

Non-Born-Oppenheimer calculations of the pure vibrational spectrum of HeH+

Very accurate calculations of the pure vibrational spectrum of the HeH(+) ion are reported. The method used does not assume the Born-Oppenheimer approximation, and the motion of both the electrons and the nuclei are treated on equal footing. In such an approach the vibrational motion cannot be decoupled from the motion of electrons, and thus the pure vibrational states are calculated as the states of the system with zero total angular momentum. The wave functions of the states are expanded in terms of explicitly correlated Gaussian basis functions multipled by even powers of the internuclear distance. The calculations yielded twelve bound states and corresponding eleven transition energies. Those are compared with the pure vibrational transition energies extracted from the experimental rovibrational spectrum.     

Traveling waves in systems of oscillators on 2D-lattices

A system of differential equations that describes the dynamics of an infinite system of linearly coupled nonlinear oscillators on a 2D-lattice is considered. The exponential estimate of the solution and some results on the existence of periodic and solitary traveling waves are obtained.     

Change of exciton-phonon interaction in layered ferroelastic crystals (Cs3Bi2I9)

The half-width of exciton absorption band (n=1) of Cs₃Bi₂I₉ layered ferroelastic crystals was studied carefully as function of temperature in the range from 5 to 300 K. For the first time, we have found a new physical effect: change of exciton-phonon interaction (from weak to strong) in the same sample as temperature increases. It was established that the temperature value T^*=150 K may be considered as characteristic one, below which a crystal loses the nature of layered substance. The effect is explained using a model that takes into account the reconstruction of the crystal lattice from non-layered to layered one.     

Explicitly correlated Gaussian calculations of the (2)D Rydberg states of the boron atom

Accurate non-relativistic variational calculations are performed for the seven lowest members of the (2)D Rydberg series (1s(2)2s2p(2), and 1s(2)2s(2)nd, n = 3, [ellipsis (horizontal)], 8) of the boron atom. The wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian basis functions and the effect of the finite nuclear mass is directly included in the calculations allowing for determining the isotopic shifts of the energy levels. The Gaussian basis is optimized independently for each state with the aid of the analytic energy gradient with respect to the Gaussian parameters. The calculations represent the highest accuracy level currently achievable for the considered states. The computed energies are compared with the available experimental data.