Statistical simulation of the energy spectra of field-emission electrons

Random energies of electrons that escape from the source in the course of field emission are simulated using energy spectra. A relationship of the random values of total energy and the energy related to the normal (with respect to surface) component of momentum is established. A family of quadrature formulas needed for the integration of the distribution density of particles is analyzed. A hypothesis on the compliance of selected random energies with desired distribution laws is statistically tested.     

Mechanism for the formation of molecular clusters under ion sputtering

The mechanism for the formation of molecular Si _n O _2n+1 ^? clusters above the surface during the recombination of ions, atoms, and molecules independently sputtered in individual cascades is presented. Clusters form when sputtering products Si, O, SiO and SiO₂ (monomers) join the active anion O^? successively as a result of pair collisions between them. The joining of monomers involves different combinations of them; in this case, the (Si _n O_2n+1)^? group is formed and consists of monomers with the same masses, but with different monomer compositions in the chain (combinatorial synthesis).     

Manifestation of the anticrossing of energy levels in EPR spectra of spin clusters

The EPR spectra of a system of two coupled spins with strongly anisotropic g factors have been calculated. It has been shown that the spectra can exhibit an additional absorption line in the vicinity of the energy level anticrossing. The emergence of this line is caused by strengthening of the off-resonance absorption in the anticrossing region.     

Theoretical determination of electron binding energy spectra of anionic magnesium clusters

A recently developed accurate scheme for converting the single-particle eigenenergies of the density functional theory into electron binding energies is used to compute the spectra of electron binding energies in and . The computations are performed for different isomeric forms of the clusters using both pseudopotential and all-electron treatments. The results are compared with the data derived from electron photodetachment experiments, and the role of the different isomers in the interpretation of these data is examined.     

On the average energy of sputtered particles

Summary The correct expression for the average energy of sputtered particles in the linear regime has, for the first time, been derived. The theoretical results are compared with recent data from computer simulation studies and it is shown that the average sputtered energy can only be evaluated by precisely determining both the maximum energy and the threshold of the sputtered particles.

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Riassunto è stata derivata per la prima volta l’espressione corretta nel regime lineare dell’energia media delle particelle emesse da solidi durante bombardamento ionico. I risultati teorici sono stati confrontati con alcuni dati ottenuti recentemente mediante simulazione al calcolatore. è stato inoltre evidenziato che l’energia media delle particelle emesse può essere calcolata in modo preciso solo se si determinano contemporaneamente l’energia massima delle particelle emesse e la soglia per il processo di emissione.

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Резюме Впервые выводится правильное выражение для средней энергии распыленных частиц в линейном режиме. Теоретические результаты сравниваются с недавними данными численного моделирования на ЭВМ. Показывается, что средняя распыленная энергия может быть оценена только при условии, если точно определены одновременно максимальная энергия распыленных частиц и порог для процесса распыления.

     

On the energy distribution of sputtered dimers

A theoretical expression is obtained for the energy distribution of sputtered dimers from crystal surfaces. The derivation is based on a model where the atoms which constitute a dimer, are sputtered independently from the crystal according to their respective single particle energy distribution functions. Two neighbouring atoms are then supposed to form a dimer if the sum of their initial relative kinetic energy and potential energy is less than zero. A comparison with experimental results for K₂ and KI sputtered from polycrystalline K and KI surfaces respectively, shows a good agreement.     

Decay rate constants of sputtered vanadium oxide clusters

Results from studying the emission and fragmentation of V _n O _m ^± clusters sputtered from a vanadium surface by Xe⁺ ions at O₂ pressures of P = 4–5 × 10^?3 Pa are presented. The average decay rate constants of V _n O _m ^± clusters for major fragmentation channels are determined. It is shown that the decay rate constants for clusters of similar stoichiometry do not depend on their charge states.     

Statistical hadronization model and transverse momentum spectra of hadrons in high energy collisions

A detailed analysis of transverse momentum spectra of several identified hadrons in high energy collisions within the canonical framework of the statistical model of hadronization is performed. The study of particle momentum spectra requires an extension of the statistical model formalism used to handle particle multiplicities, which is described in detail starting from a microcanonical treatment of single hadronizing clusters. Also, a new treatment of extra strangeness suppression is presented which is based on the enforcement of fixed numbers of pairs in the primary hadrons. The considered center-of-mass energies range from to 30 GeV in hadronic collisions ( and Kp) and from 15 to 35 GeV in collisions. The effect of the decay chain following hadron generation is accurately and exhaustively taken into account by a newly proposed numerical method. The exact conservation at low energy and the increasing hard parton emission at high energy bound the validity of the presently taken approach within a limited center-of-mass energy range. However, within this region, a clear consistency is found between the temperature parameter extracted from the present analysis and that obtained from fits to average hadron multiplicities in the same collision systems. This finding indicates that in the hadronization process the production of different particle species and their momentum spectra are two closely related phenomena governed by one parameter. Received: 31 October 2001 / Published online: 15 February 2002     

Influence of type of bonds in compounds on the mechanism of the sputtered excited particles formation under ion bombardment

A review of studies of the radiation of the excited particles ejected from metals and its chemical compounds under ion bombardment are presented. The observed features of ion-photon emission (IPE) are analyzed taking into account the physical-chemical parameters of solids and spectroscopic parameters of ejected excited particles. Different mechanisms of the ejected excited particles formation for the explanation of the experimental data are considered.     

Energy spectra of atoms sputtered by KeV light-ion bombardment

A calculation has been made for the sputtering of heavy targets by KeV light-ion bombardment. The calculation is based both on linear transport theory and on the assumption that only primary recoiling atoms are candidates for the sputtering process. The energy spectra calculation predicts the experimentally observed peak shift towards lower velocities than those obtained by standard linear cascade theory.     

Statistical model of coexisting multiquark clusters

A model for describing nuclear matter consisting of different multiquark clusters is constructed. Special attention is paid to the case when nucleons (3-quark clusters) coexist with 6-, 9- and 12-quark clusters. A detailed analysis of statistical properties for this mixture is presented over the whole density-temperature plane. The dependence of the results on the mass parametrization is also checked.     

Global energy minima of molecular clusters computed in polynomial time with semidefinite programming

The global energy minima of pure and binary molecular clusters with 5-12 particles interacting pairwise are computed in polynomial time as a function of only the two-particle reduced density function (2-RDF). We derive linear matrix inequalities from the classical analogue of quantum N-representability constraints to ensure that the 2-RDF represents realistic N-particle configurations. The 2-RDF reformulation relaxes a combinatorial optimization into a convex optimization that scales polynomially in computer time. Clusters are optimized with a code for large-scale semidefinite programming developed for the quantum representability problem [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)10.1103/PhysRevLett.93.213001].     

Theoretical investigation on isomer formation probability and free energy of small C clusters

Molecular dynamics simulations and free energy calculations are employed to investigate the evolution,formation probability,detailed balance,and isomerization rate of small C cluster isomer at 2500 K.For C10,the isomer formation probability predicted by free energy is in good agreement with molecular dynamics simulation.However,for C20,C30,and C36,the formation probabilities predicted by free energy are not in agreement with molecular dynamics simulations.Although the cluster systems are in equilibrium,detailed balance is not reached.Such results may be attributed to high transformation barriers between cage,bowl,and sheet isomers.In summary,for mesoscopic nanosystems the free energy criterion,which commonly holds for macroscopic systems in dynamic equilibrium,may not provide a good prediction for isomer formation probability.New theoretical criterion should be further investigated for predicting the isomer formation probability of a mesoscopic nanosystem.     

Statistical analysis of composite spectra

We consider nearest-neighbor spacing distributions of composite ensembles of levels. These are obtained by combining independently unfolded sequences of levels containing only few levels each. Two problems arise in the spectral analysis of such data. One problem lies in fitting the nearest-neighbor spacing distribution to the histogram of level spacings obtained from the data. We show that the method of Bayesian inference is superior to this procedure. The second problem occurs when one unfolds such short sequences. We show that the unfolding procedure generically leads to an overestimate of the chaoticity parameter. This trend is absent in the presence of long-range level correlations. Thus, composite ensembles of levels from a system with long-range spectral stiffness yield reliable information about the chaotic behavior of the system.