1 Introduction

Existence of the doubly ionized nitrogen (N III) spectral lines in a great number of various hot stars spectra make them interesting for diagnostic purposes (Wesemael et al. 1985; Underhill 1995). They are transmitters of information about the physical conditions in the place of their birth. Knowledge of the Stark broadening parameters (the width and the shift) of the spectral lines enables modelling various physical processes in the hot star plasmas where the Stark broadening is the principal pressure broadening mechanism. The intensive spectral lines from the lower multiplets are very convenient for experimental investigations (Underhill 1995). In the case of the N III spectra these lines belong to the 3s-3p (multiplet No. 1) and to the 3p-3d (No. 2) transitions. A number of papers (Popovic et al. 1975; Källne et al. 1979; Purcell & Barnard 1984; Puric et al. 1987; Glenzer et al. 1994a; Blagojevic et al. 1996) deals with the Stark FWHM (full-width at half intensity maximum, w) of these lines. It is evident that existing experimental results of the w show mutually scatter, up to the factor 4, especially in the case of the 3s-3p transition (Glenzer et al. 1994a; Blagojevic et al. 1996). On the other hand, only two papers deal with the N III lines Stark shift (d) measurements (Puric et al. 1988; Blagojevic et al. 1996), to the knowledge of the authors (Fuhr & Lesage 1993, and references therein). The aim of this paper is to provide some new data on several Stark widths and shifts of doubly ionized nitrogen spectral lines belonging to 3s-3p and 3p-3d transitions in the range of a: 30 000 K-54 000 K electron temperature (T). Namely, knowledge of the Stark width and shift dependence upon the electron temperature in the plasma is, also, of a great importance for testing their theoretical predictions based on various approaches. Our measured values of Stark widths and shifts have been compared to the existing experimental results and theoretical predictions based on the semiclassical and modified semiempirical approaches initiated by Dimitrijevic & Konjevic (1980, 1981a,b) presented by Blagojevic et al. (1996).