Electron impact excitation ofHg+

Crossed beams of electrons and ${\mathrm{Hg}}^{+}$ ions have been employed to measure absolute cross sections for 165.0-nm emission, corresponding to the transition ${\mathrm{Hg}}^{+}(6p^{2}P_{\frac{3}{2}}^{0})\ensuremath{\rightarrow}{\mathrm{Hg}}^{+}(6s^{2}S_{\frac{1}{2}})$. The emission cross section, which is nearly identical to the excitation cross section for ${\mathrm{Hg}}^{+}(6p^{2}P_{\frac{3}{2}}^{0})$ near threshold, has a value of about 1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at the 7.51-eV threshold, rises to a maximum of 2.26 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 13 eV, and falls to 0.64 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 274 eV. The cross section exhibits considerable structure in the energy region from threshold to the onset of the first cascade ($7s^{2}S_{\frac{1}{2}}$) at 11.9 eV; this structure is likely due to interference from autoionizing states of neutral Hg. The total uncertainty at a "good" confidence level is about 18%, taken as the quadrature sum of random uncertainty (5% at 90% confidence level) with systematic uncertainties (17% at a level equivalent to 90% confidence level). At threshold, the Gaunt-factor formula of Seaton predicts a value of about 3 times that measured, but the two converge to within about 15% for electron energies ranging from 13 to 274 eV. The results are also in reasonable agreement with a semiclassical Gryzinski-type calculation for energies above several times threshold. The data give an emission cross section of (2.8 \ifmmode\pm\else\textpm\fi{} 0.5) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 6.8 eV for 194.2 nm ($6p^{2}P_{\frac{1}{2}}^{0}\ensuremath{\rightarrow}6s^{2}S_{\frac{1}{2}}$). Analysis of data taken with some metastable $6{s}^{2}^{2}D$ ions in the target beam indicates that the mean cross section for excitation of the $6s^{2}P_{\frac{3}{2}}^{0}$ level from the $6{s}^{2}^{2}D$ metastable states is larger than that for excitation from the $6s^{2}S_{\frac{1}{2}}$ ground state. Additional measurements of 398.4-nm emission ($6p^{2}P_{\frac{3}{2}}^{0}\ensuremath{\rightarrow}6{s}^{2}^{2}D_{\frac{5}{2}}$) yield a cross section of about 6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}19}$ ${\mathrm{cm}}^{2}$ near threshold, and a branching ratio $\frac{(^{2}P_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}S_{\frac{1}{2}})}{(^{2}P_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}D_{\frac{5}{2}})}$ of $\frac{350}{1}$.