摘要:

The electron ionization in ion‐atom collisions is studied by using the Continuum Distorted Wave‐Eikonal Initial State model. Some relevant aspects of this theory are reviewed. Two‐center effects are analyzed. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50096

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Fundamental mechanisms for electron production in ion‐atom collisions are reviewed. Electron emission is discussed in terms of categories involving zero, one and two atomic centers. The centers are defined as heavy nuclear charges which interact strongly with the ejected electron. The binary encounter process, attributed to zero or one center, is dominated by two‐body kinematics. The soft collision process, which corresponds to dipole transitions with small momentum transfer, is associated with one center. Various two‐center phenomena are discussed. Electron capture to continuum, giving rise to a cusp‐shaped peak near 0°, is viewed as a focusing effect in the Coulomb field of the receding projectile. Two‐center electron emission, involving the effect of both target and projectile charge on the outgoing electrons, is shown to be visible at forward as well as at backward emission angles. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50097

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Beginning with his initial studies of the angular dependence of the spectra of electrons emitted in ion‐atom collisions, the first measurements to provide a detailed and comprehensive description of the collisional ionization process, M. Eugene Rudd contributed to an impressive list of ‘‘firsts’’ in the study of collision physics. In 1963, Gene published the first observation of a two‐center phenomena in collision physics, although it was several years before the features he observed in the spectra of ejected electrons were clearly interpreted as contributions from electron‐capture‐to‐the‐continuum, a two‐center phenomena. He contributed firsts in studies of doubly differential cross sections, inner‐shell‐ and auto‐ionization, interactions involving dressed projectiles, and interactions of ions and photons with surfaces. He also refined the experimental techniques to provide data of improved reliability in many areas where others had made pioneering studies including measurements of doubly‐differential cross sections for incident electrons and total‐ionization and charge‐transfer cross sections for ion impact. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50098

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Gene Rudd’s analysis of doubly differential cross sections for the ionization of He atoms by proton impact suggested that electrons were being carried along by the proton for a short period of time after being ejected from the target region. Normally, this would represent an electron capture event in which an excited state of atomic hydrogen is formed. Because the electron ends up ionized it was recognized that these states of the proton must be continuum states. This insight was confirmed by observations of the continuum electron capture (CEC) cusp when the electron velocity equals the proton velocity in the final state. The impact of this idea upon the theory of ionization at high energies is reviewed. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50100

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The use of ion‐atom collisions to study the autoionizing states of atoms was discovered by Rudd while a professor at Concordia College in Moorhead, MN. The technique has been used to study the autoionizing transitions in target atoms and projectile ions, and to study the collisions that form the excited states. The doubly excited states of helium are still being investigated in collision experiments within the framework of the few‐body problem. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50101

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Modeling of differential and total ionization cross sections by electron impact is reviewed. A new theoretical model that does not depend on any empirical or arbitrary parameters is described. The prototype of this new model was proposed by Rudd and was originally based on the binary‐encounter theory. The model has been improved by replacing a part of the binary‐encounter theory with the dipole contribution as prescribed by the Bethe theory. The current model, henceforth referred to as the binary‐encounter‐dipole (BED) model, reproduces known singly differential and total ionization cross sections for small atoms and molecules accurately. The possibility of extending the BED theory to doubly differential cross sections as well as to proton‐impact ionization cross sections is discussed. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50102

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Reactions of target excitation by impact of bare ions are studied. Two‐center distortion effects have been theoretically predicted at low intermediate collision energies for impact of heavy projectiles on light targets. Recent experiments support the existence of these effects. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50103

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Evidences of double scattering mechanism in ion‐atom ionization are presented. The observed structures are explained by a simple process in which an electron initially bound to the target suffers a binary encounter with the incoming projectile and then a second collision with the target core. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50104

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

There exist several inherent difficulties involved with measurements of low‐energy electrons emitted in ion‐atom collisions, such as stray magnetic fields and detector efficiencies. However, there exists one experimental problem that tends to be ignored in the literature: secondary‐electron emission and reflection due to electrons impacting the back plate of an analyzer. A straightforward analysis reveals that even small amounts of electron plate‐impact contamination can lead to significant spectral distortions in measurements of low energy electrons. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50081

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The charge state fractionsFqof slow Cuq+ions formed by one‐electron capture in single collisions between protons and Cu atoms forq=1 to 5 have been measured in the energy range 70–730 keV amu−1. Measured fractions have been satisfactorily described in terms of an independent electron model of ionization of the 4sand 3delectrons. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50082

出版商:AIP    

年代:1996

数据来源: AIP