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In this paper, we present the electron-impact ionization cross sections for eight highly charged Na-like ions in the range 18 ≤ Z ≤ 39 calculated by means of a distorted-wave Born exchange approximation method including relativistic corrections. Direct ionization from the ground and excited states (n = 3-5) is calculated. For the ground state, contributions due to excitation-autoionization are also calculated, taking account of branching ratios and configuration interaction. A systematic study of the dependence of the cross sections on impact energy and nuclear charge is carried out for the direct ionization of all states and for excitationautoionization. The results of the calculations are fitted by empirical formulas to facilitate use in practical applications; the fitted values are found to be in good agreement with the calculated results. An accurate empirical formula for calculating ionization rates is also given. C

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