Search

A study was conducted to analyze the thermodynamical properties of small neutral sodium fluoride clusters by Monte Carlo and molecular dynamics simulations. The steepest descent quenching technique was utilized to determine the minima on the potential energy surface along Monte Carlo trajectories. Experimental results addressed concerns associated with a general thermodynamical definition of the liquid phase in finite systems.

In this article we present the first measurement of the electric dipole susceptibility of one excess electron Na[sub n]F[sub n - 1] clusters. The static electronic polarizability and the permanent electric dipole of these clusters have been calculated with a one-electron model. Experimental values for the susceptibility are clearly related to the calculated values of the permanent dipole. The size evolution of the dipole moments is interpreted in terms of the interplay between the lattice and electron properties. This study outlines that the response of the cluster to the electric field cannot be fully understood with only equilibrium structure calculations and that the coupling between the permanent dipole and the vibrational motion of the cluster has to be taken into account. [ABSTRACT FROM AUTHOR]

A one-electron pseudopotential model is used to calculate the excited states of Na[SUBn]F[SUBn-1] clusters in the range 2⩽n⩽29. The transition dipole moments are derived to determine the vertical absorption lines from the ground state. Monte Carlo simulations based on the Franck-Condon principle are also achieved to obtain finite temperature absorption spectra. The analysis of ground and excited orbitals in various situations illustrates the rather simple nature of the excitations which are interpreted through an analogy with s-p type transitions in atoms. The influence of electron localization in the initial state is pointed out. Comparison of the simulated spectra with experimental data provides additional keys to understand and discuss the relationship between structure, electron localization, and spectroscopic properties. [ABSTRACT FROM AUTHOR]

NanFn-1 clusters are produced in a laser vaporization source. They are ionized by one-photon or resonant two-photon ionization, and detected in a high resolution time of flight mass spectrometer. By scanning the ionization wavelength, it is possible to obtain ionization potentials and absorption spectra of these clusters, for n ranging from 2 to 42. The results we obtain show many discrepancies with the cuboid model, which has proven valid for small sizes. The possible origin of these disagreements is discussed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Rydberg spectrum of Na2 has been shown previously to alternate when increasing energy between ‘‘stroboscopic fringes’’ which correspond to a well known separable Hund’s coupling case (a), and a complex, unidentifiable intermediate coupling. We use this system as a prototypic example to test some current ideas on the correspondence between classical chaos and properties of quantum spectra. We first determine the phase space structure and transition to chaos in classical mechanics. We then determine the change in line intensities and level spacing statistics in quantum mechanics. We show that this system has the expected behavior in the semiclassical limit in the presence of classical chaos, except for a peculiarity in level spacing statistics, but that this behavior is not a signature of chaos, since the same system shows similar behavior for some values of the parameters which correspond to a nonchaotic situation in classical mechanics. We discuss also some problems related to the nonvalidity of the semiclassical limit. [ABSTRACT FROM AUTHOR]

We have measured the single and double photoionization efficiency of Hgn mass selected clusters as a function of photon energy between 30 and 110 eV for masses ranging from n=1 to 36 for the singly ionized and from n=5 to 70 for the doubly ionized clusters, using the light beam issued from a wiggler at the BESSY synchrotron. The results show in all cases a spectrum similar to the 5d→εf shape resonance previously observed in the isolated atom. In contrast, the expected 5p→6p transition allowed by hybridization of the 6s and 6p orbitals is not observed. We also compared the mass spectra of singly and doubly charged mercury clusters ionized by electron impact (30–90 eV) to those of clusters ionized by synchrotron radiation (30–70 eV). We found that the ratio Hg2+n/Hg+n was higher for photoionization at low energy and for electron impact ionization at high energy. Finally, we estimated the critical stability size of the triply charged clusters. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In some poïetic narratives, artists in their perceptive experience happen upon a solution to an artistic problem when they least expect it and in unexpected places, after a time of emptiness due to a delay or unwanted circumstance. From Leonardo da Vinci to the surrealist painter Max Ernst, we analyze the relations between those empty times – of various psychological and circumstantial sorts – that immediately follow and have the capacity of seizing an unforeseen opportunity and integrating it into their artistic approach. A stylistic and dramatic turn to better highlight the fertile moment of serendipity? A rhetoric of irony that turns a dreary period into a moment of intense creativity? A much-needed rest to better sharpen the awareness that ensues? Or a dive into a visually-rich unconscious, that sometimes finds mind-boggling solutions? These empty moments, whatever their contents, probably play a much greater part than it appears in the serendipitous approach of number of artists. So, even if we exclude sanctifying their activity, we can consider their seemingly empty times as holding the promise of artistic serendipity.