M1 and E2 transitions in ArII

Systematically enlarged multiconfiguration Dirac-Fock wavefunctions have been used to calculate the transition energies, oscillator strengths, emission rates and branching ratios for the fine-structure forbidden M1 and E2 transitions between the levels of the low-lying 3s(2) 3p(5), 3s3p(6), 3p(4)3d and 3p(4)4s configurations in AT II. Large wavefunction expansions had to be applied since these transitions happened to be very sensitive with respect to configuration interactions and relativistic effects. By applying a sufficiently large expansion for the wavefunctions, however, our theoretical data agree well with those obtained in precision measurements and, therefore, might be used in the identification of further (observed) lines. We also report the energies and rates for the dipole-allowed El transitions, for which a number of previous experiments and computations are available from the literature.