Efimov states in asymmetric systems

The conditions for occurrence of the Efimov effect is briefly described using hyperspherical coordinates. The strength of the effective hyperradial $\rho^{-2}$ potential appearing for two or three large scattering lengths is computed and discussed as function of two independent mass ratios of the three constituent particles. The effect is by far most pronounced for asymmetric systems with three very different masses. One Efimov state may by chance appear in nuclei. Many states could be present for systems with one electron and two neutral atoms or molecules. Estimates of the number of states and their sizes and energies are given.Comment: 7 pages, 3 figure

Density of Superfluid Helium Droplets

The classical integral cross sections of large superfluid 4He_N droplets and the number of atoms in the droplets (N=10^3-10^4) have been measured in molecular beam scattering experiments. These measurements are found to be in good agreement with the cross sections predicted from density functional calculations of the radial density distributions with a 10-90 % surface thickness of 5.7\AA. By using a simple model for the density profile of the droplets a thickness of about 6-8\AA is extracted directly from the data.Comment: 27 pages, REVTeX, 5 postscript figure

Pinning of quantized vortices in helium drop by dopant atoms and molecules

Using a density functional method, we investigate the properties of liquid 4He droplets doped with atoms (Ne and Xe) and molecules (SF_6 and HCN). We consider the case of droplets having a quantized vortex pinned to the dopant. A liquid drop formula is proposed that accurately describes the total energy of the complex and allows one to extrapolate the density functional results to large N. For a given impurity, we find that the formation of a dopant+vortex+4He_N complex is energetically favored below a critical size N_cr. Our result support the possibility to observe quantized vortices in helium droplets by means of spectroscopic techniques.Comment: Typeset using Revtex, 3 pages and 5 figures (4 Postscript, 1 jpeg

Transition from molecular complex to quantum solvation in OCS(He)_N

We present quantum calculations of the rotational energy levels and spectroscopic rotational constants of the linear OCS molecule in variable size clusters of 4He, using spectral evolution quantum Monte Carlo methods that allow excited states to be accessed without nodal constraints. The rotational constants of OCS are found to decrease monotonically from the gas phase value as the number of helium atoms increases to N=6, after which the average constant increases to saturation at a value in excellent agreement with experimental measurements made on significantly larger clusters (N>1000). The minimum is shown to indicate a transition from a molecular complex to a quantum solvated molecule, with the former characterized by floppy but near rigid behavior, while the latter is characterized by non-zero permutation exchanges and a smaller extent of rigid coupling.Comment: 4 pages, 1 figure, submitted to Phys. Rev. Lett. on July 18,200

Emergence of four dimensional quantum mechanics from a deterministic theory in 11 dimensions

We develop a deterministic theory which accounts for the coupling of a high dimensional continuum of environmental excitations (called gravonons) to massive particle in a very localized and very weak fashion. For the model presented Schrodinger's equation can be solved practically exactly in 11 spacetime dimensions and the result demonstrates that as a function of time an incoming matter wave incident on a screen extinguishes, except at a single interaction center on the detection screen. This transition is reminiscent of the wave - particle duality arising from the "collapse" (also called "process one") postulated in the Copenhagen-von Neumann interpretation. In our theory it is replaced by a sticking process of the particle from the vacuum to the surface of the detection screen. This situation was verified in experiments by using massive molecules. In our theory this "wave-particle transition" is connected to the different dimensionalities of the space for particle motion and the gravonon dynamics, the latter propagating in the hidden dimensions of 11 dimensional spacetime. The fact that the particle is detected at apparently statistically determined points on the screen is traced back to the weakness and locality of the interaction with the gravonons which allows coupling on the energy shell alone. Although the theory exhibits a completely deterministic "chooser" mechanism for single site sticking, an apparent statistical character results, as it is found in the experiments, due to small heterogeneities in the atomic and gravonon structures

High-quality variational wave functions for small 4He clusters

We report a variational calculation of ground state energies and radii for 4He_N droplets (3 \leq N \leq 40), using the atom-atom interaction HFD-B(HE). The trial wave function has a simple structure, combining two- and three-body correlation functions coming from a translationally invariant configuration-interaction description, and Jastrow-type short-range correlations. The calculated ground state energies differ by around 2% from the diffusion Monte Carlo results.Comment: 5 pages, 1 ps figure, REVTeX, submitted to Phys. Rev.

Electrochemical synthesis of peroxomonophosphate using boron-doped diamond anodes

A new method for the synthesis of peroxomonophosphate, based on the use of boron-doped diamond electrodes, is described. The amount of oxidant electrogenerated depends on the characteristics of the supporting media (pH and solute concentration) and on the operating conditions (temperature and current density). Results show that the pH, between values of 1 and 5, does not influence either the electrosynthesis of peroxomonophosphate or the chemical stability of the oxidant generated. Conversely, low temperatures are required during the electrosynthesis process to minimize the thermal decomposition of peroxomonophosphate and to guarantee significant oxidant concentration. In addition, a marked influence of both the current density and the initial substrate is observed. This observation can be explained in terms of the contribution of hydroxyl radicals in the oxidation mechanisms that occur on diamond surfaces. In the assays carried out below the water oxidation potential, the generation of hydroxyl radicals did not take place. In these cases, peroxomonophosphate generation occurs through a direct electron transfer and, therefore, at these low current densities lower concentrations are obtained. On the other hand, at higher potentials both direct and hydroxyl radical-mediated mechanisms contribute to the oxidant generation and the process is more efficient. In the same way, the contribution of hydroxyl radicals may also help to explain the significant influence of the substrate concentration. Thus, the coexistence of both phosphate and hydroxyl radicals is required to ensure the generation of significant amounts of peroxomonophosphoric acid

Localized helium excitations in 4He_N-benzene clusters

We compute ground and excited state properties of small helium clusters 4He_N containing a single benzene impurity molecule. Ground-state structures and energies are obtained for N=1,2,3,14 from importance-sampled, rigid-body diffusion Monte Carlo (DMC). Excited state energies due to helium vibrational motion near the molecule surface are evaluated using the projection operator, imaginary time spectral evolution (POITSE) method. We find excitation energies of up to ~23 K above the ground state. These states all possess vibrational character of helium atoms in a highly anisotropic potential due to the aromatic molecule, and can be categorized in terms of localized and collective vibrational modes. These results appear to provide precursors for a transition from localized to collective helium excitations at molecular nanosubstrates of increasing size. We discuss the implications of these results for analysis of anomalous spectral features in recent spectroscopic studies of large aromatic molecules in helium clusters.Comment: 15 pages, 5 figures, submitted to Phys. Rev.

The design of organic catalysis for epoxidation by hydrogen peroxide

The potential of various organic species to catalyze epoxidation of ethene by hydrogen peroxide is explored with B3LYP/6-31G* DFT calculations