Ramsauer-Townsend effect in the electron loss fromH0colliding with heavy atoms

Abstract

The emission pattern of loosely bound projectile electrons is strongly dependent on the target species. For 0.5 MeV hydrogen colliding with krypton we observe large variations in the intensity of these electrons as a function of emission angle. There are also large changes in the energy and width of the electron loss peak associated with these intensity variations. These features are closely related to the Ramsauer-Townsend scattering of free electrons and can be interpreted within the electron impact approximation, a model which successfully combines free electron scattering by the heavy target with the Compton profile of the initially bound projectile electron.PACS numbers: 34.50.FaOne of the fundamental processes occurring in heavy ion collisions is the ejection of electrons. A study of their energy and angular distribution provides a unique insight into the collision dynamics and into the atomic structure of the collision partners [1]. With the availability of recent more accurate measurements one has a sensitive test of traditional theoretical models and those being newly developed. An essential feature in the spectrum arising from projectiles which carry electrons into the collision is in "the electron loss peak" which was independently discovered by Burch, Wieman, and Ingalls [2] and Wilson and Toburen [3] and identified to originate from these projectile electrons. Since the peak is located at an energy which approximately corresponds to the energy of the outermost projectile electron in the target rest frame, one of the earliest interpretations was based on the idea that electron loss might be treated as an elastic collision between the projectile electron and the target atom. Free electron-atom scattering (as reviewed by, e.g., Bransden and McDowell [4]) is a field which has been thoroughly investigated in order to get detailed information about the electronic properties of the target. As early as the 1920s, Ramsauer [5] and Townsend and Bailey [6] discovered pronounced structures in the energy dependence of the elastic scattering cross section from heavy rare gas atoms. Later investigations [7,8] have revealed that these intensity variations arise from deep minima in the angular dependent differential cross sections. These structures, which can be reproduced with the help of close-coupling calculations [9,10], have been interpreted in terms of interference effects between the different partial waves contributing to the scattering amplitude. The absence of structures for helium targets and the increase of the number of minima with increasingly heavier rare gases (at fixed impact energy) could then readily be explained by the number of partial waves required: only a few for He, but some tens for the heaviest gases.Menendez and Duncan [11] were the first to discover structures in the angular dependent singly differential cross section in the case of clothed ion impact. Somewhat surprisingly, subsequent measurements of doubly differential electron loss cross sections from hydrogen or helium impact on all ...

The importance of continuum eigenstates in electron spectroscopy

“…(5)) has to be used. A peaking version of the SB2, as first introduced by Hartley and Walters [39], is well able to describe the increase in peak energy and the decrease in width for 9, --) 0 which is seen in experiment [17].…”

“…x 1 c&q) I 'a( E, -e; -u2/2 -qv), (17) matches the width of the bound electron's momentum distribution (pp [38]. However, although in the H + Kr system the Ramsauer structures are not clearly visible in the spectra, they cause large variations in the position and width of the electron loss peak near those angles which are related to minima in the differential cross section for elastic electron scattering on Kr (Fig.…”

“…At backward emission angles, this peak is related to the binary encounter peak by a frame transformation 1161 and hence shows similar properties as the BE peak when the collision system is reversed. In particular, an anomalous behaviour in the EL peak position and width for very heavy targets has been found [17].…”

Diffraction effects in electron loss from incident on Ar at 78 keV

“…The observation of the strong diffraction effects in the binary-collision peak were followed by a systematic study of the electron-loss mechanism performed at the University of Frankfurt. The measurements consisted of doubly differential distributions for H and He projectiles at high collision energies, incorporating coincidence techniques in order to separate the electron-loss channels (Heil et al 1991a, b, 1992, Kuzel et al 1992, 1993, 1994. The electron-loss peak, when integrated over the electron energy, yielded the single differential cross section or angular distribution that showed the presence of minima.…”

Breakup of positronium in a collision with aLi+ion

“…Most of the earlier experiments [2][3][4][5][6][7][8][9][10][11] and consequently theories [12][13][14][15][16][17][18][19] on the projectile ionization concentrated on bare , partially stripped [ 2-6, 12, 13, 16-19 ] or neutral heavy projectiles [ 7-11, 14, 15 ] for which a cusp shaped peak was observed in the emitted electron energy spectrum at around e v ( velocity of the electron ) p v ≈ ( velocity of the positron ). This peak was attributed to the electron loss from the projectile ion / atom into its low -lying continuum, usually referred to as the ELP peak .…”