The effect of atomic chemical bonding under fast ion stopping in solids

Abstract

The calculation of ion stopping cross-sections in compounds was carried out by applying Bragg and Kleeman's rule /1/ However, in a series of experimental papers / 2 , 3/ (and in those quoted in /3/) the inadequacy of this rule for a variety of binary compounds has been shown.Earlier Brandt /4, 5/ considered the effect of atomic chemical bonding on the mean ionization potential comprised in the Bethe-Bloch equation for fast ion energy loss.In the present paper an atomic chemical bonding effect both on heavy ion stopping cross-sections and on the deviations from the above rule is shown for ionic crystals.Indeed, at an ionic velocity lower than that of outer electrons, the electrons of the outermost shell of target atoms provide the main contribution to the electronic energy loss cross-sections, S . The spatial distribution and the bonding energy of these electrons accounts for the oscillatory dependence of S both on the projectile atomic number Z compounds the character of the outer electron distribution essentially depend6 on the bond type between compound constituents. One can define the additivity rule of stopping cross-sections with the account of chemical bonding in compouods as e e and that of the monoatomic target Z2 /6, 7/. In the case of 1'where AS can acquire any sign. 0bIn monoatomic solid and gas targets inelastic ion stopping croes-sections a r e well described by the modified Firsov theory /7/, where it i s assumed that free atoms a r e localized in regular lattice sites. The electron configuration wave functions were used in the form of Slater orbitals / 8 / .