Semiempirical formulae for electron impact excitation and ionization of hydrogenic ions

Simple, semiempirical formulas are given for collision strengths and rate coefficients for n - n-prime transitions in highly charged hydrogenic ions or for transitions between excited levels of nonhydrogenic ions treated in a hydrogenic approximation with the use of screening constants. The corresponding formulas for electron impact ionization cross sections and rate coefficients are also given with the effects of lowering of the continuum included. Results obtained with these formulas are compared with a large amount of accurate data now available. It is concluded that for hydrogenic ions with nuclear charge number 2 = 10 or greater they are generally accurate to within 25 percent for the conditions of major interest for plasma modeling, and usually the accuracy is somewhat better.