Spectroscopy on somegsymmetry states inH2and determination of the ionization potential

Term values of 14 levels of $\mathrm{EF}{}^1{\Sigma }_g^{+}\mathrm{}(v=19\mathrm{}),$ $\mathrm{GK}{}^1{\Sigma }_g^{+}\mathrm{}(v=0\mathrm{}),$ $I{}^1{\Pi }_g\mathrm{}(v=0\mathrm{}),$ and $J{}^1{\Delta }_g\mathrm{}(v=0\mathrm{})\mathrm{}$ states in ${\mathrm{H}}_2$ have been calibrated in a two-step laser excitation experiment with an accuracy of $0.006\hspace{0.5em}{\mathrm{cm}}^{-1}.$ Combined with literature data on inter-Rydberg transitions these highly accurate values on g symmetry levels yield an independent determination of the ionization potential in ${\mathrm{H}}_2$ at $124417.476\hspace{0.5em}\mathrm{}\left(12\right)\mathrm{}\hspace{0.5em}{\mathrm{cm}}^{-1},$ which is consistent with previous experimental values and with ab initio calculation.