6 Discussion

In order to compare measured and calculated Stark FWHM and shift values, the theoretical Stark FWHM and shift dependences on the electron temperature, together with the values of other authors and our experimental results, at an electron density of 10²³ m^-3 are presented graphically in Figs. 4 and 5.

Figure 4: Stark FWHM (W in 0.1 nm) dependence on the electron temperature (T) for the most investigated O III spectral lines belonging to various transitions at 1023 m-3 electron density. SCPF, our calculations by using the semiclassical perturbation formalism. $\bullet$, our experimental results and those of other authors: $\triangle$, Platisa et al. (1975); $\square$, Puric et al. (1988a); $\nabla$, Blagojevic et al. (2000). SE, SEM, G and GM denote theoretical W values (see text). +, calculations by Hey & Bryan (1977). INS denote estimated W values (Djenize et al. 1990; Djenize & Labat 1996; Djenize 2000). The error bars include the uncertanties of the width and electron density measurements. $<\lambda >$ is the mean wavelength in the multiplet

The first O III W values were calculated on the basis of various approximations initiated by Griem (1974); Hey & Bryan (1977) and Dimitrijevic & Konjevic (1980). Thus, SE and SEM denote the results of semi-empirical (Griem 1968) and modified semi-empirical predictions using Eqs. (4), (5) and Eqs. (7)-(10), respectively from Dimitrijevic & Konjevic (1981). G and GM denote W values obtained on the basis of the simplified semiclassical method (Griem 1974). For the GM values the low temperature part is modified (Dimitrijevic & Konjevic 1980). The estimated Wvalues, based on the obtained regularities of the Stark FWHM along an oxygen isonuclear sequences (INS), have been taken from Djenize (1990, 1996, 2000).

Figure 5: Stark shift (d in 0.1 nm) dependence on the electron temperature (T) for the OIII spectral lines belonging to various transitions at 1023 m-3electron density. SCPF, our calculations by using the semiclassical perturbation formalism. $\bullet$, our experimental results and those of other authors: $\square ,$ Puric et al. (1988b). The error bars include the uncertanties of the shift and electron density measurements. $<\lambda >$ is the mean wavelength in the multiplet

On the basis of the Tables 1, 2, and Fig. 4 one can conclude that our measured ($W_{\rm m}$) and calculated (SCPF) Stark FWHM values are in satisfactory mutual agreement (within $\pm 13\%$ in average). We notice, also, fair agreement between $W_{\rm m}$ and $W_{\rm G}$ and $W_{\rm INS}$ values. Values W measured earlier (Puric et al. 1988a; Blagojevic et al. 2000) agree, also, with $W_{\rm SCPF}$, $W_{\rm G}$ and $W_{\rm INS}$ calculated values within the accuracy of experiments (up to $\pm 15\%$) and uncertainties of the approximations (up to $\pm 30 \%$).

Our calculated Stark shift values are small and have a negative sign. The measured $d_{\rm m}$ values are, in most of the cases (see Table 2), equal to zero. The only exception is the 408.11 nm OIII line which we have measured and, also, it has a calculated shift different from zero. It turns out that the calculated d values of the particular wavelengths are approximately constant over a wide range of the electron temperatures from 20 000 K up to 500 000 K.