Ion-Pair States in Triplet Molecular Hydrogen

An experimental search is underway to observe the long range triplet ionic states H$^{\mathrm{+}}$ H$^{\mathrm{-}}$ of molecular hydrogen. Resonantly enhanced multi-photon ionization of the metastable c $^{\mathrm{3}}\prod _{\mathrm{u}}^{\mathrm{-\thinspace }}$ 2p$\pi $ state is used access to the R(1)nd1 n$=$21 Rydberg state that serves as an intermediate stepping stone state to probe the energy region above the ionization limit with a second tunable laser photon. The metastable state is prepared by electron capture of 6 keV H$_{\mathrm{2}}^{\mathrm{+}}$ ions in potassium in a molecular beam. Formation of the H$^{\mathrm{+}}$ H$^{\mathrm{-}}$ triplet configuration involves triplet excited states of the H$^{\mathrm{-}}$ ion, especially the 2p$^{\mathrm{2}} \quad^{\mathrm{3}}$P$^{\mathrm{e}}$ state, the second bound state of H$^{\mathrm{-}}$ predicted to exist with a lifetime long compared to typical auto ionization lifetimes but not yet observed experimentally. Details of the experiment and preliminary results to date will be presented at the conference.