摘要:

Mesoscopic systems are under intense theoretical and experimental development. New theoretical concepts are required which patch the statistical assumptions of random and incoherent systems to coherent quantum mechanics. The field is made even more compelling because of the potential for devices which are so small that quantum coherences and ballistic transport are important. We focus here on the quantum corral experiments involving Fe adatoms placed one at a time on the surface of Cu(111). ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49822

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Some of the ion‐atom processes relevant to plasma heating by fast neutral beams, modelling of edge plasmas and plasma diagnostics in current and next‐step Tokamak devices are considered. Results of measurements on a number of selected processes involving charge transfer, ionization and excitation are discussed in relation to theoretical predictions. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49813

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The advent of third generation synchrotron radiation sources has opened up exciting possibilities for research. The characteristic features of these sources will be presented and the road towards diffraction limited storage ring sources and Free Electron Lasers for the soft‐ and hard X‐ray regime will be outlined. The large impact of the new sources on atomic physics will be demonstrated by the discussion of most recent experiments. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49767

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A survey is given of the spectroscopy and dynamics studies of superexcited molecules by means of electron‐ and photon‐impact methods with particular emphasis on their dissociation dynamics. Topics chosen from recent progress in these studies are 1) comparison of electron‐ and photon‐impact studies with each other, 2) dissociation dynamics of H2in doubly excited states, 3) dissociation dynamics of inner core excited states of molecules, e.g., C2H2and O2, and 4) absolute photoabsorption, photoionization, and photodissociation cross sections, and photoionization quantum yields of molecules. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49784

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Recent synchrotron radiation studies of inner‐shell excitation and associated ionic decay spectroscopies of molecular beams of clusters of rare gas atoms and molecules are reviewed. The dependence of Ar(2p) spectra on the size of argon clusters provides information on cluster structure and the length scale over which the cluster properties change from atom‐like to solid‐like. Ion‐ion and photoelectron‐photoion‐photoion coincidence studies (charge separation mass spectrometry) probe charge separation mechanisms in rare gas and molecular clusters. The inner‐shell spectroscopy and ionic fragmentation of three isomericcloso‐carboranes species are reported. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49803

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Angular distributions of fragment ions produced from linear molecules photoexcited to inner‐shell excited states reflect symmetry of these excited states because the production of the ions is very fast compared to the rotational motion of the molecules. Some examples have been shown for the &pgr;* state, Rydberg orbital excited states and the shape resonance of diatomic and linear triatomic molecules using a rotatable time‐of‐flight mass spectrometer and monochromatized synchrotron radiation. Kinetic energy distributions of fragment ions from inner‐shell hole states have been determined at several photon energies using time‐of‐flight spectra and a simulation fitting calculation. These distributions give a considerable difference between neutral excited and ionized states, indicating that the dissociation pathway from the &pgr;* excited state is different from that at the ionized state. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49804

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Various theoretical studies have investigated correlations between the two continuum electrons in photo‐double‐ionization of He. Near‐threshold, intermediate and high energy studies have been performed using different experimental methods to test the corresponding predictions. Recent developments in studies of double photoionization of He are presented from below the double‐ionization threshold to 12 keV. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49806

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Recent theoretical developments have led to an unprecedented capability to describe complex photoionization processes. In many systems that exhibit nonperturbative electron correlations, theory can reproduce or predict experimental spectra, essentially to spectroscopic accuracy. The aim of this review is to show howR‐matrix techniques can determine the parameters of multichannel quantum defect theory. These parameters, in turn, determine the experimental observables that can be measured either with or without an external field present. I also summarize some relatively recent developments, such as the development ofR‐matrix methods to describe some two‐electron ejection processes. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49807

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Experiments on double photoionization, where the two outgoing electrons are selected in angle and energy before being detected in coincidence, have started in 1991 on xenon and krypton. During the past four years they have been extended to lighter rare gases including helium, and a general understanding of the observed angular patterns has started to emerge. In the present paper we report on such recent measurements in helium, neon and argon, obtained with a multidetection apparatus and in the so called ‘‘coplanar’’ geometry. We try to analyse the physical effects underlying the shapes of the various angular patterns which are presented. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49808

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Cross sections for electron excitation of helium metastable levels to higher levels have been measured. When the metastable atoms are generated by a hollow cathode discharge, the measurements are limited to incident electron energies below 16 eV. An alternate target source utilizes the charge‐exchange reactions between He+ions and alkali atoms which yield predominately He atoms in the metastable levels. With this target source cross section measurements have been made with electron energies up to 300 eV. Recently laser‐cooled atom traps have been used to measure electron scattering cross sections and electron‐impact ionization cross sections. This technique may be well suited for studying electron collisions with excited atoms. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49809

出版商:AIP    

年代:1996

数据来源: AIP