Multipole expansion analysis of electron loss to the continuum for He⁺ions colliding with rare gases

Abstract

We present an analysis of electron loss to the continuum (ELC) for 1.6-2.8 MeV He+ colliding with He, Ne and Ar using the first six terms of the multipole expansion method. We give absolute values for E,, and discuss the way in which the method of analysis influences the values of the dipole and quadrupole parameters. Our dipole parameter is slightly positive for the He target and becomes progressively more negative for Ne and Ar. Our quadrupole parameter is slightly positive for He and Ne and nearly zero for Ar. For HeC+ He the magnitude of E,, and its velocity dependence are in reasonable quantitative agreement with a recent theoretical calculation based on the second Born approximation. However our dipole and quadrupole parameters are both more positive than predicted.

The importance of continuum eigenstates in electron spectroscopy

“…The data [28] have not been measured on an absolute scale, and hence are normalised to theory. Comparison of the cusp shape parameter B, for Xe and Ar with absolute data [12,14,15] indicates that the SB2 theory slightly overestimates experiment (within a factor of 2). The cusp shape parameters are defined through the expansion of the doubly differential cross section in terms of electron momentum IQ = k, -v and ejection angle 0; in the projectile reference frame with E, = kf2/2 and Pl a Legendre polynomial.…”

“…2 depicts the target dependence of the shape parameter p, = B,,/B,, (which is a measure for the cusp asymmetry) in the case of 0.4 MeV/amu He+ impact. Unfortunately, the /3i data extracted at different laboratories [12,14,28,29] for a given target differ strongly from each other. This may be related to the sensitivity of pi to small features in the spectra close to the cusp maximum which are strongly influenced by the detector transmission function, but may have only a minor physical meaning.…”

“…(16), the initial-state energy l ,r' has been neglected. From the interrelation (14) it follows that for heavy target atoms, the Ramsauer structures will also influence the electron loss peak. In effects from the Ramsauer minimum at 135" for the Kr target 1361 are hidden, but they become prominent if the projectile charge is artificially increased to 2, = 1.5 (Fig.…”

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 .…”

Fragmentation of positronium in collision with Li ion including electron loss to the continuum

“…For most of the earlier experiments [2][3][4][5][6][7][8][9][10] and consequently theories [11][12][13][14] on ELC concentrated on bare, partially stripped [2][3][4][5][6][8][9][10][11][12][13][14] or neutral heavy projectiles [7], a distinct signature of a cusp/peak was observed in the emitted electron energy spectrum at around v e (velocity of the electron) ≈ v p (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 ELC peak.…”