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We have calculated collision strengths for electron excitation of the 3s23p4 3Pg,,,2, 'D; and 'Sg levels of Ar 111 using the R-matrix method. We included the five states 3s23p4 'Pe, 'De, ' S e and 3s3p5 3P0, 'Po, which we represented by configuration interaction wavefunctions. These wavefunctions yield oscillator strengths for allowed transitions between the levels which are in good agreement with the experimental values. Reactance matrices were obtained in LS coupling and were transformed using JAJOM to give the fine-structure collision strengths. The latter have been averaged over a Maxwellian electron velocity distribution to give the effective collision strengths, for temperatures from 4000 to 24 000 K. Our calculated electron excitation rates are up to 50% larger than previous values at 10 000 K due to resonance structure in the collision strengths.

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