Recombination measurements at low energies with Ar16+ and Ar18+ ions in a dense, cold electron target

Recombination of multiply charged ions with electrons at very low relative energies has become a major topic of interest, due to the observation of rates which are enhanced beyond the expectations for radiative recombination. We present results for Ar16+ and Ar18+ ions from systematic measurements along the argon isonuclear sequence using a high density cold electron beam target (n(e) = 7 x 10(9) cm(-3)) at the UNILAC of GSI. The transverse and longitudinal temperatures of the electron beam were determined from DR resonance features observed with metastable Ar16+(2(3)S) ions, The rate at E-rel = 0 for radiative recombination of completely stripped Ar18+ calculated with electron beam temperatures kT(parallel to) = 0.002 eV, kT(perpendicular to) = 0.2 eV amounts to alpha = 10(-9) cm(3) s(-1). This is exceeded by nearly a factor of 10 by the rate measured in experiments with Ar18+ ions.