Investigation of cross sections for the formation and destruction of negative boron ions

Abstract

The electron loss and electron capture cross sections σi,i+m and σi,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H2, He, N2, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear charge Zt of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Ztt1/2. A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the charge i. It describes the dependence of the electron capture cross section σi,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σi,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σi,i−1 exhibit substantially nonmonotonic variation with Zt, increasing on average as Zt1/3.