The energy levels for P IV lines have been taken from Martin et al. (1985). Oscillator strengths have been calculated by using the method of Bates & Damgaard (1949) and the tables of Oertel & Shomo (1968). For higher levels, the method described by Van Regemorter et al. (1979) has been used.

**Table 2:** Present semiclassical Stark full widths at half maximum (WDSB)
in Å
compared with the calculations of Dimitrijevic (1988a,b)
by using
the modified semiempirical approach (Dimitrijevic &
Konjevic 1980),
Griem's semiempirical approach (Griem 1968),
symplified semiclassical approach
(Eq. (526) in Griem 1974) and its modification
(Dimitrijevic &
Konjevic 1980)

In addition to electron-impact full halfwidths and shifts,
Stark-broadening parameters due to proton-, and He III- impacts
have been calculated. Our results for 114 P IV multiplets are shown in
Table 1 (published only in electronic form),
for perturber densities
and temperatures . We also specify a
parameter *c* (Dimitrijevic & Sahal-Bréchot
1984), which
gives an estimate for the maximum perturber density for which
the line may be treated as isolated when it is divided by the
corresponding full width at half maximum. For
each value given in Table 1, the collision
volume (*V*) multiplied by the perturber density (*N*) is much
less than unity and the impact approximation is valid
(Sahal-Bréchot 1969a,b). Values for *NV* > 0.5
are not given and
values for are denoted by an asterisk.
When the impact approximation is not valid, the ion
broadening contribution may be estimated by using
quasistatic approach (Sahal-Bréchot 1991 and Griem 1974).
In the region between where neither of these two approximations is
valid, a unified type theory should be used. For example in Barnard et
al. (1974), a simple analytical formula for such a case is given. The
accuracy of the results obtained decreases when broadening by ion
interactions becomes important.

In Table 2 (click here), present semiclassical Stark full widths at half maximum (WDSB) in Å are compared with the calculations in Dimitrijevic (1988a,b) by using the modified semiempirical approach (Dimitrijevic & Konjevic 1980), Griem's semiempirical approach (Griem 1968), simplified semiclassical approach (Eq. (526) in Griem 1974) and its modification (Dimitrijevic & Konjevic 1980). One can see that the best agreement is with the results obtained by using the simplified semiclassical approach.

For further development and refinement of the theory, the corresponding experimental data will be very useful.

*Acknowledgements*

This work is a part of the project ``Astrometrical, Astrodynamical and Astrophysical Investigations", supported by Ministry of Science and Technology of Serbia.

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