Measurement of the field-induced dielectronic-recombination-rate enhancement of O 5 + ions differential in the Rydberg quantum number n

The influence of electromagnetic fields on the dielectronic recombination of ${\mathrm{O}}^{5+}$ ions has been measured at the Stockholm heavy ion storage ring CRYRING. The experimental energy range covered all $2\stackrel{\ensuremath{\rightarrow}}{s}2p$ $\ensuremath{\Delta}n=0$ resonances. Electric fields up to 600 V/cm were applied and a noticeable enhancement of the dielectronic recombination cross section as a function of electric-field strength was observed. Field ionization of highly exited Rydberg states was used to investigate the enhancement of the recombination rate for two narrow bands of n states ranging from $n\ensuremath{\approx}19\char21{}22$ and from $n\ensuremath{\approx}23\char21{}25.$ The experimental data are compared to theory. After applying a field-ionization model to the calculations, the field-free spectra show good agreement with the experimental data. Although experiment and theory show the same trend of increasing strength of dielectronic recombination with increasing external electric field and with increasing n, quantitative discrepancies remain.