Dielectronic recombination forCa+via4s→4pexcitation

Dielectronic recombination has been directly observed with a crossed, modulated electron and calciumion beams technique. The stabilizing photons (about 397 nm) and the 500-eV Rydberg-state neutral atoms were detected in coincidence following electron-impact excitation in the vicinity of doubly excited ${\mathrm{Ca}}^{**}$ resonant states below the ${\mathrm{Ca}}^{+}\left(4p{}_{}{}^2{}_{}{}^{}P\right)$ excited ionic state. A peak ${\mathrm{Ca}}^{+}\left(4P{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\right)$ excitation cross section of 1.7 × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ was measured simultaneously with the peak dielectronic recombination cross section of 1.8 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ which is about double the Burgess-Mertz theoretical value.