Accurate energies for the low-lying levels of singly ionizedHg198

A 3.34-m plane-grating spectrograph has been used to measure the wavelengths of 11 lines of singly ionized ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ emitted by an electrodeless discharge lamp in the region 1942–7944 Å. The uncertainty varies from ±0.0003 to ±0.0015 Å. From these wavelengths, accurate values were determined for all levels of the 5$d^{10}$6s, 6p, 6d, 7s, 7p, and 5$d^9$6$s^2$ configurations and for four levels of the 5$d^9$6s6p configuration. By using existing isotope-shift data, values of wavelengths and energy levels for natural Hg i i were deduced. Accurate values for 12 lines of Hg i i in the region 893–2026 Å were calculated from the energy levels.