3 Theory

For evaluation of Stark widths and shifts of non - hydrogenic lines of ionized atoms, various theoretical approaches have been used, see e.g. Griem (1974). For example, in the case of the singly ionized atoms semiclassical and quantum-mechanical approaches have been applied. However, both approaches involve considerable labor, especially the quantum-mechanical method. Griem (1968) suggested a simple semiempirical impact approximation based on Baranger's (1958) original formulation together with the use of an effective Gaunt-factor approximation proposed by Seaton (1962) and Van Regemorter (1962). For singly ionized atoms this semiempirical formula agrees with experiment on the average to within $\pm$50% (Griem 1974). In order to apply semiempirical approach (Griem 1968) to the lines of multiply ionized atoms Dimitrijevic & Konjevic (1980) made certain modifications to this method. Then, this approach was applied to the evaluation of multiply charged ion Stark width, see e.g. Dimitrijevic & Konjevic (1980). Apart from this application the modified semiempirical formula (SEM) was used for singly charged ions as well, see e.g. Dimitrijevic (1996).

In order to test the applicability of SEM for evaluation of plasma widths of singly charged ions we shall calculate the Stark FWHM's of 460.354 nm NII line and compare them with measured values. Electron impact width have been calculated on the basis of the modified semiempirical approximation (Dimitrijevic & Konjevic 1980). The necessary atomic data were taken from Wiesse et al. (1966).