  We report the first detection of radio recombination lines (RRLs) of ions
heavier than helium. In a highly sensitive multi-band (12--50 GHz) line survey
toward Orion KL with the TianMa 65-m Radio Telescope (TMRT), we successfully
detected more than fifteen unblended $\alpha$ lines of RRLs of singly ionized
species (XII) recombined from XIII. The Ka-band (35--50 GHz) spectrum also
shows tentative signals of $\beta$ lines of ions. The detected lines can be
successfully crossmatched with the the rest frequencies of RRLs of CII and/or
OII. This finding greatly expands the connotation of ion RRLs, since before
this work only two blended lines (105$\alpha$ and 121$\alpha$) of HeII had been
reported. Our detected lines can be fitted simultaneously under assumption of
local thermodynamic equilibrium (LTE). An abundance of CIII and OIII of
8.8$\times$10$^{-4}$ is obtained, avoiding the complexities of optical/infrared
observations and the blending of RRLs of atoms. It is consistent with but
approaches the upper bound of the value (10$^{-4}$--$10^{-3}$) estimated from
optical/infrared observations. The effects of dielectronic recombination may
contribute to enhancing the level populations even at large $n$. We expect
future observations using radio interferometers could break the degeneracy
between C and O, and help to reveal the ionization structure and dynamical
evolution of various ionized regions.
