Perturbed structure of molecular hydrogen near the second dissociation limit

The region of the second dissociation limit of ${\mathrm{H}}_2$ converging to H(1s)+H(2s,2p) has been investigated using high-resolution double-resonance spectroscopy through the E,${\mathit{F}}^1$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ state. Transitions to the very high vibrational levels of the ${\mathit{B}}^1$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$, B’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$, and ${\mathit{C}}^1$ ${\mathrm{\Pi }}_{\mathit{u}}$ states have been measured with 0.02-${\mathrm{cm}}^{\mathrm{-}1}$ accuracy. Numerous perturbations and unexpected transitions are observed as far as 10 ${\mathrm{cm}}^{\mathrm{-}1}$ below the dissociation limit. This complex structure, still not fully understood, arises from a combination of electronic, fine-structure, and hyperfine interactions.