Soft-electron-peak asymmetry.

Abstract

We study the asymmetry characteristics of the low-velocity electronic emission in the bare ion-atom collision. These electrons form the so-called soft electron peak (SE peak) in the double-differential cross section. We parametrize the SE peak, expanding the double-differential cross section in Legendre polynomials. We extend previous studies determining the coefficients of the expansion by fitting available experimental data for ${\mathrm{C}}^{6+}$, ${\mathrm{O}}^{8+}$, and ${\mathrm{Ne}}^{10+}$ colliding with He at 5 MeV/amu incidence energy. We discuss the accuracy of that fitting and the convergence of the expansion and compare the fitting with predictions of the continuum distorted-wave-eikonal initial state theory. We confirm the existence of an asymmetry in the forward-backward direction in the electron distribution. We analyze these coefficients and former results as a function of projectile charge and impact energy, looking for scaling laws in these variables. We have found a law for the zeroth-order coefficients in Legendre polynomial expansion.