Yu. A. Tashaev

A semiempirical method for determining the cross sections for the loss of electrons by fast multiply charged ions

Abstract This paper describes a semiempirical method for calculang the cross sections σi,i+m for the loss of one and several electrons by fast multielectron ions, which is based on the results of an analysis of experimental data and theoretical calculations. In the proposed method, from the known values of σi,i+m for various ions one can find the cross sections for the loss of an individual electron σnl which are practically independent of the number of electrons qnl in a shell nl. This makes it possible to calculate the cross sections σnl and the cross sections for the increase in charge, Si = Σmσi,i+m, for any other ion. The values of the cross sections σi,i+m are then extracted from those of Si in accordance with the relative probability Pm for the loss of m electrons. It is suggested that in the region of extremely high ion velocities the cascade filling of inner-shell vacancies is the predominant mechanism for the removal from a multielectron ion of several electrons. Using this method the cross sections σi,i+m (m = 1–5) have been calculated for fast ions of iodine and uranium in nitrogen.

Cross sections for the loss of the outer 1s, 2s and 2p electrons for fast multicharged ions

The cross sections sigma i,i+m for the loss of m electrons (m=1, 2, 3) for light ions in helium, nitrogen, neon and argon are measured at ion velocities V=2.7, 4 and 8*108 cm s-1. The values of sigma i,i+m are used to obtain the cross sections sigma i(nl) for outer 1s, 2s and 2p electron loss. It has been shown that in the range of V<or approximately=4*108 cm s-1 the cross sections sigma i(2p) for 2p electron loss are 1.2-3 times the cross sections sigma i(1s) and sigma i(2s) for 1s and 2s electrons at the same electron binding energy. The relations between these cross sections are in qualitative agreement with the variations of the electron binding energy when the electrons are promoted to the quasimolecular states.

Decrease in the observed excited-ion electron capture cross sections due to autoionization

From measurements of the cross sections for electron capture by fast helium-like ions N5+ produced by three different methods, it has been found that by increasing the number of metastable particles in an ion beam from 3% to 40% the electron capture cross section is decreased approximately twice. The use of results of previous investigations clearly shows that this decrease is due to autoionization of lithium-like ions N4+ produced from electron capture. It is suggested that the autoionization mechanism may also account for the previously observed anomalies in the electron capture cross sections for P5+, Br7+ and I7+ ions and the decreased charge-exchange cross sections for He+ and N+ metastable ions.