1 Introduction

A number of problems in solar and stellar physics, plasma physics and technology (see e.g. Griem 1974) depends on a comprehensive set of reliable data on the influence of impacts with charged particles on spectral line shapes, i.e. on the Stark broadening parameters. For example, Stark broadening parameters for multiply charged ions are needed for the modelling and theoretical considerations of subphotospheric layers (Seaton 1997), as well as for the examination of radiative transfer. Such data for multiply charged ion lines are of additional interest as well due to the development of soft X-ray lasers, where Stark broadening data are needed to calculate gain values, to model radiation trapping and to consider photoresonant pumping schemes (see e.g. Griem & Moreno 1990; Fill & Schöning 1994). Of course such data are also useful for the rafinement and checking of theory, as well as for the consideration of systematic trends along isoelectronic sequences. Scandium and titanium in various ionization stages are present in stellar plasma. For example Rogerson & Ewell (1985) have found 7 Ti IV lines in the $\tau$ Sco spectrum. One should mention as well that Stark broadening parameters for 10 scandium III and 10 Titanium IV multiplets, have been calculated recently within the semiclassical perturbation approach by Dimitrijevic & Sahal-Bréchot (1992).

This paper is the twenty first of a series devoted to the research of Stark broadening parameters of spectral lines of multicharged ions (see Dimitrijevic & Sahal-Bréchot 1995 and references therein, as well as Dimitrijevic & Sahal-Bréchot 1996a,b, 1997, 1998a-e). As the continuation of our project (see e.g. Dimitrijevic 1996) to make available to astrophysicists and physicists an as large as possible set of reliable semiclassical Stark broadening data needed for the investigation, diagnostics and modeling of various plasmas in stellar and solar physics, abundance determinations, opacity calculations, modeling and consideration of subphotospheric layers, diagnostics and investigation of laboratory plasma,as well as for laser physics, fusion research, and various devices as e.g. light sources, we have calculated within the semiclassical-perturbation formalism (Sahal-Bréchot 1969a,b), electron-, proton-, and He III-impact line widths and shifts for 4 Sc X, 10 Sc XI, 4 Ti XI and 27 Ti XII multiplets.