ALBERT

Notes: To gain insight into the mechanism of Na(3p)2P3/2→2P1/2 fine-structure transitions induced by collision with He, we monitor the expectation values of the orbital- and spin-angular momentum vectors, l and s, as a function of time along the trajectory, using a semiclassical formalism. In a typical collision, 〈s〉 remains nearly space-fixed while 〈l〉 precesses about the rotating internuclear axis. Thus, in the interaction region, the projection of 〈l〉 onto the internuclear axis, 〈λ〉, remains nearly constant, and the molecular alignment of the orbital is preserved. We show how equations of motion for the classical analogues of these expectation values agree qualitatively with the quantum equations of motion. A qualitative comparison is also made with the Cs–He system for which the spin–orbit coupling is much stronger. We calculate cross sections for Na(2P3/2)+He→Na(2P1/2)+He as a function of the alignment of the excitation laser polarization with respect to the asymptotic relative velocity vector. For stationary pumping of the excited F=3 hyperfine level, this calculation predicts that the perpendicular alignment gives a cross section which is larger by a factor of 1.8 than that obtained by parallel alignment.

Notes: In this paper we present results of coupled channel quantum scattering calculations of the alignment selected j=3/2→ j=1/2 fine structure changing integral cross section for Na(2P)+He. This cross section has in the past been written in terms of a coherent sum of partial wave amplitudes, but we have found that it can be expressed in terms of an incoherent sum of partial cross sections, each labeled by the total angular momentum J and by parity. It is also possible to define an alignment selected wave function for each J such that the azimuthal average of the square of this wave function projected onto each final state is proportional to the magnitude of the partial cross section into that state. This J labeled wave function is thus clearly related to the physical measurables, and we have used it to determine propensities for preservation of asymptotically prepared alignment during collisions. Using a potential surface based on Pascale's ab initio calculations, we find that the alignment ratio σ⊥/σ(parallel) is an increasing function of energy, with a value less than unity at low energy (〈0.01 eV), but increasing quickly to a value of about 2.0 at 0.04 eV and then more slowly at higher energy, up to a value of 2.7 at 0.2 eV (the highest energy considered). Above 0.02 eV, both the alignment ratio and the alignment selected integral cross sections are in good agreement with values calculated in an accompanying semiclassical study (Kovalenko, Leone, and Delos).An examination of the J labeled alignment selected scattering wave functions and of the expectation values of 〈Ω〉, 〈Λ〉, and 〈Σ〉 indicates that at low J when the initial state is prepared with (parallel) polarization, the dominant state at short range is Σ while with ⊥ polarization the dominant state is Π (i.e., asymptotic alignment is preserved). By way of contrast, this propensity for alignment preservation is not seen if fluxes or probability densities associated with alignment selected wave functions labeled by the initial orbital quantum number l (rather than J) are considered. This l labeled result is in accord with recent work by Pouilly and Alexander, but the lack of alignment preservation in this case has no relationship with the alignment cross sections, or with the alignment selected plane wave scattering wave function, since the l labeled wave functions must be coherently combined to generate this information. The orbital scrambling found for the l labeled solutions thus is not related to measurable properties, and instead the correct picture is provided by the J labeled solutions, which do show preservation of alignment. We find that even in the J labeled picture, alignment preservation does not by itself guarantee any specific trend in the alignment ratio for the fine structure transition.

Notes: Nonlinear evolution of one-dimensional planar perturbations in an optically thin, radiatively cooling medium in the long-wavelength limit is studied numerically. The accepted cooling function generates, in thermal equilibrium, a bistable equation of state P(ρ). The unperturbed state is taken close to the upper (low-density) unstable state with infinite compressibility (dP/dρ=0). The evolution is shown to proceed in three different stages. At the first stage, pressure and density set in the equilibrium equation of state, and velocity profile steepens gradually, as in the case of pressure-free flows. At the second stage, those regions of the flow where anomalous pressure (i.e., with negative compressibility) holds create a velocity profile sharper than in the pressure-free case, which in turn results in formation of a very narrow (short-wavelength) region where gas separates the equilibrium equation of state and pressure equilibrium sets in rapidly. At this stage, the variation in pressure between the narrow dense region and the extended environment does not exceed more than 0.01 of the unperturbed value. At the third stage, gas in the short-wavelength region reaches the second (high-density) stable state, and pressure balance establishes through the flow, with pressure equal to the one in the unperturbed state. In external (long-wavelength) regions, gas forms slow isobaric inflow toward the short-wavelength layer. The duration of these stages decreases when the ratio of the acoustic time to the radiative cooling time increases. The limits in which nonlinear evolution of thermally unstable long-wavelength perturbations develops in isobaric regime are obtained. © 1999 American Institute of Physics.

Notes: The design of "KRION-C'' with an energy of up to 80 keV and preliminary results on the ionization of sulfur and argon ions are presented. The cryogenic electron beam ionizer "KRION-C'' was used as an ion source for the first run with sulfur relativistic nuclei at the accelerating facility of the Laboratory of High Energies (LHE) in Dubna.

Notes: The design of the electron-beam ion source (EBIS) "Krion-S'' on the high voltage (HV) platform of the preinjector of the LINAC LU-20 and some results of accelerating argon and krypton ions up to 5 Mev/u are presented. The gas mixing (working gas and Ne) by original technology has been used for the "ion cooling'' procedure. The cryogenic ionizator Krion-S is used as an ion source for multicharged ions with mass charge ratio band 0.35–0.5 at the accelerating facility "NUCLOTRON'' of the Laboratory of High Energies (LNE) JINR in Dubna. © 1996 American Institute of Physics.

Notes: A simple system for beam positioning and spatial distribution diagnostics based on a cooled charge coupled device (CCD) camera, scintillation screen, and optics has been developed. Standard methods of recording beam profiles are different for low and high intensity beams, which complicates readout techniques. The main advantage of our system is its adaptability for intensity range 103–1012 particles/cm2/pulse. The system was tested at the Dubna synchrophasotron complex. Protons and nuclei beam profile and position monitoring in mentioned intensity range and energy range of 10 MeV to 10 GeV was provided. A CCD camera is used in wavelengths interval 400–1100 nm. The hardware, software, and cryogenics of this system are described. Effects of fixed pattern noise and dependence of nonuniformity of response on wavelength are shown and some results of beam diagnostic are presented.

Notes: With near-infrared gating and improved light collection geometry, the entire fluorescence band can be upconverted in a broad range of 10 000 cm−1 without readjusting optical elements, thus allowing measurements with a single pump-gate scan. Monitoring of the pump-induced white light continuum provides for the time correction of the up-converted fluorescence spectra. The overall time resolution is then limited by the pump-gate cross correlation. The technique is illustrated with the femtosecond evolution of fluorescence from two molecular probes in solution. © 2001 American Institute of Physics.

Notes: We developed a self-consistent three-dimensional reference interaction site model integral equation theory with the molecular hypernetted chain closure (SC-3D-RISM/HNC) for studying thermochemistry of solvation of ionic solutes in a polar molecular solvent. It is free from the inconsistency in the positions of the ion–solvent site distribution peaks, peculiar to the conventional RISM/HNC approach and improves the predictions for the solvation thermodynamics. The SC-3D-RISM treatment can be readily generalized to the case of finite ionic concentrations, including the consistent dielectric corrections to provide a consistent description of the dielectric properties of ion–molecular solution. The proposed theory is tested for hydration of the Na+ and Cl− ions in ambient water at infinite dilution. An improved agreement of the ion hydration structure and thermodynamics with molecular simulation results is found as compared to the conventional RISM/HNC treatment. © 2000 American Institute of Physics.

Notes: We study the hydration structure and free energy of several conformations of Met-enkephalin in ambient water by employing the one-dimensional (1D) as well as three-dimensional (3D) reference interaction site model (RISM) integral equation theories, complemented by the hypernetted chain (HNC) closure with the repulsive bridge correction (RBC). The RBC contribution to the excess chemical potential of solvation is calculated by means of the thermodynamic perturbation theory (TPT), which crucially reduces computational burden and thus is especially important for a hybrid algorithm of the RISM with molecular simulation. The 3D-RISM/HNC+RBC-TPT approach provides improved prediction of the solvation thermodynamics and gives a detailed description of the solvation structure of a biomolecule. The results obtained are discussed and compared to those following from the 1D-RISM/HNC theory. The latter yields physically reasonable results for the conformational stability of biomolecules in solution, which is further improved by adding the 1D-RBC. The modified, 1D-RISM/HNC+RBC-TPT integral equation theory combined with the simulated annealing or generalized-ensemble Monte Carlo simulation methods is capable of reliable prediction of conformations of biomolecules in solution with due account for the solvent effect at the microscopic level. © 2000 American Institute of Physics.

Notes: We have developed a self-consistent description of an interface between a metal and a molecular liquid by combination of the density functional theory in the Kohn–Sham formulation (KS DFT) for the electronic structure, and the three-dimensional generalization of the reference interaction site model (3D RISM) for the classical site distribution profiles of liquid. The electron and classical subsystems are coupled in the mean field approximation. The procedure takes account of many-body effects of dense fluid on the metal–liquid interactions by averaging the pseudopotentials of liquid molecules over the classical distributions of the liquid. The proposed approach is substantially less time-consuming as compared to a Car–Parrinello-type simulation since it replaces molecular dynamics with the integral equation theory of molecular liquids. The calculation has been performed for pure water at normal conditions in contact with the (100) face cubic centered (fcc) surface of a metal roughly modeled after copper. The results are in good agreement with the Car–Parrinello simulation for the same metal model. The shift of the Fermi level due to the presence of water conforms with experiment. The electron distribution near an adsorbed water molecule is affected by dense water, and so the metal–water attraction follows the shapes of the metal effective electrostatic potential. For the metal model employed, it is strongest at the hollow site adsorption positions, and water molecules are adsorbed mainly at the hollow and bridge site positions rather than over metal atoms. Layering of water molecules near the metal surface is found. In the first hydration layer, adsorbed water molecules are oriented in parallel to the surface or tilted with hydrogens mainly outwards the metal. This orientation at the potential of zero charge agrees with experiment. © 1999 American Institute of Physics.