Observation of Enhanced Electron-Ion Recombination Rates at Very Low Energies

A strong enhancement of electron-ion recombination over expected rates at sub-eV relative energies is revealed for highly charged ions. Measured ${\mathrm{Ne}}^{10+}$ and ${\mathrm{Ar}}^{13+}$ recombination rates were found to be enhanced at low (<1 meV) energies by factors of 4 and 10 over theoretical predictions of radiative recombination rates, respectively. It is shown that the majority of the enhancement in ${\mathrm{Ar}}^{13+}$ is caused by very low lying $\Delta n=0\mathrm{}$ dielectronic recombination resonances; nevertheless, the nonresonant contributions to the measured recombination rates for both systems were found to be significantly higher than predicted by presently available models.