Observations of millimeter wavelength radio recombination lines (mm-RRLs) are used to search for HII regions in an unbiased way that is complementary to many of the more traditional methods previously used (e.g., radio continuum, far-infrared colors, maser emission). The mm-RRLs can be used to derive physical properties of HII regions and to provide velocity information of ionized gas. We carried out targeted mm-RRL observations (39<= principal quantum number (n) 40km/s) revealing significant turbulent motions within the ionized gas; in the past, such wide linewidths were found toward very compact and dense HII regions. We find that the systemic velocity of the associated dense molecular gas, traced by H^13^CO^+^(1-0), is consistent with the mm-RRL velocities and confirms them as embedded HII regions. We also find that the linewidth of the H^13^CO^+^(1-0) emission is significantly wider than those without mm-RRL detection, indicating a physical connection between the embedded H II region and their natal environments. We also find a correlation between the integrated fluxes of the mm-RRLs and the 6cm continuum flux densities of their radio counterparts (the correlation coefficient, {rho}, is 0.70). By calculating the electron densities we find that the mm-RRL emission is associated with HII regions with n_e_0.03pc. We detected mm-RRLs toward 178 clumps and identified eight new HII region candidates. The broad mm-RRL from nine clumps may indicate that they arise in very young hyper-compact HII regions. The mm-RRLs trace the radio continuum sources detected by high-resolution observations and their line parameters show associations with the embedded radio sources and their parental molecular clumps.

Cone search capability for table J/A+A/602/A37/table3 (Detail information of dust clumps that have recombination line detections)