Near-threshold structure of molecular hydrogen at the 1s + 2l dissociation limit

High-resolution measurements of molecular structure very near a dissociation limit can be used both to probe long-range atomic interactions and to make accurate determinations of dissociation energies. Our research group has investigated the H(1s) + H(2s or 2p) dissociation limit in molecular hydrogen using optical double resonance with single-mode lasers. Fig. 1 shows the general scheme of the experiment. Our measurements of bound states in H2, reported in Ref. 1, have now been extended to include the adjoining continuum and the other stable isotopomers, HD and D2. The most weakly bound levels to which transitions are seen are bound by only about 0.03 cm−1, equivalent to about 40 mK. Very sharp continuum resonances are also observed in the region just above threshold.