Photorecombination of Sc3+ and Ti4+ ions:: Search for interference effects and recombination at low energies

In search for interference between radiative and dielectronic recombination (RR and DR) absolute recombination rate coefficients for Ar-like Sc3+ and Ti4+ ions have been measured at the Heidelberg heavy ion storage ring TSR. Whereas the Sc3+ experiment suffers from statistics too poor for a line shape analysis, the Ti4+ recombination spectrum clearly does not exhibit asymmetric lineshapes due to quantum mechanical interferences as recently predicted theoretically for Sc3+ ions. The broad Ti3+(3s(2)3p(5)3d(2) F-2) DR resonance expected on the basis of multi-configuration Hartree-Fock calculations at 3.0 eV with a width of 1.3 eV appears to be shifted towards zero center-of-mass (c. m.) energy, such that its width is larger than its distance to threshold. At zero c. m. energy an unexplained recombination rate enhancement of a factor of 2 beyond the sum of RR and DR rates is observed.