On the basis of average experimental data we demonstrate scaling laws of electron-impact multiple ionization cross sections and propose expressions for the cross sections for arbitrary atoms and ions.
We present cross sections for electron-impact-induced transitions n → n ′ in hydrogen-like ions C 5+ , N e 9+ , Al 12+ , and Ar 17+ . The cross sections are computed by Coulomb-Born with exchange and normalization (CBE) method for all transitions with n < n ′ < 7 and by convergent closecoupling (CCC) method for transitions with n < n ′ < 5 in C 5+ and Al 12+ . Cross sections 1s → 2s and 1s → 2p are presented as well. The CCC and CBE cross sections agree to better than 10% with each other and with earlier close-coupling results (available for transition 1 → 2 only). Analytical expression for n → n ′ cross sections and semiempirical formulae are discussed. PACS number(s): 34.80.Kw
We present an easy to use expression for cross sections of electron-impact-induced 1s 2 nl→1s 2 nЈlЈ excitation transitions with 2рnрnЈр4 in multiply charged ions of lithium isoelectronic sequence. This expression is based on our computations by convergent close-coupling ͑CCC͒ and Coulomb-Born with exchange and normalization ͑CBE͒ methods. We show scaling of the CCC and CBE cross sections with atomic number Z and use this scaling for presentation of the cross-section data. For 6рZр30 the scaling is accurate to better than Ϯ20% at any energy except in the vicinity of resonances. Contributions from indirect excitation channels do not scale with Z; however, for calculation of excitation rates it is enough to average locally these contributions over energy and to take them into account in a frame of a general scaling-based expression for the cross sections. For excitation rates, total inaccuracy caused by all simplifications in the cross-section presentation is likely to be less than Ϯ30% even for most risky cases. This assessment is based on comparison of excitation rates, computed using our scaling-based expression for the cross sections, with the excitation rates, computed using high-resolution ͑CCC and R matrix͒ cross sections and experimental data. ͓S1050-2947͑97͒06211-2͔
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