The NaK 1 3 ⌬ state has been studied by the perturbation-facilitated optical-optical double resonance technique. Mixed singlet-triplet levels, A(2) 1 ⌺ ϩ (v A ,J)ϳb(1) 3 ⌸(v b ,J), were pumped from thermally populated rovibrational levels of the ground state, X(1) 1 ⌺ ϩ (v X ,JϮ1), using a single-mode cw dye laser. A single-mode cw Ti:Sapphire laser was then used to further excite the NaK molecules to various 1 3 ⌬(v ⌬ ,N ⌬ ,J ⌬ ) rovibrational levels which were detected by observing collision-induced 3 ⌳→a(1) 3 ⌺ ϩ fluorescence in the green part of the spectrum. The measured energies of the 1 3 ⌬(v ⌬ ,N ⌬ ) levels were fit to a Dunham expansion, and the Dunham coefficients were used to construct the RKR potential curve. Absolute numbering of the 1 3 ⌬ state vibrational levels was established by a comparison of experimental and calculated 1 3 ⌬(v ⌬ ,N ⌬ ,J ⌬ ) ←b(1) 3 ⌸(v b ,J b ) absorption line strengths. A deperturbation program was used to determine the vibration-dependent 1 3 ⌬ state spin-orbit interaction parameter. Hyperfine structure of the 1 3 ⌬ state was studied, and the Fermi-contact interaction term for this state was determined to be ϳ0.0111 cm Ϫ1 .

Double resonance spectroscopy via the EF 1 ⌺ g + , EF Ј =6,JЈ state has been used to probe the rovibrational structure of the ungerade double-well BЉB 1 ⌺ u + state of H 2 . Transitions to the BЉB 1 ⌺ u + , B = 17− 35, J =0−4 levels of the outer-well and to the B Љ B = 46− 50, J =0−4 levels of the combined inner and outer wells above the barrier have been recorded by detecting both molecular and atomic ion production as a function of energy by using a time of flight mass spectrometer. Theoretical energy calculations incorporating the most recent potential curves have been used to aid in the assignment of observed transitions. Over 70 new rovibrational term energies are reported. Where comparisons are possible, good agreement is observed between the experimental measurements reported here and those of previous measurements. While significant perturbations are observed in the energy region above the double-well barrier, assignments to states with dominant inner and outer-well characteristics can still be made. Distinct dynamical behaviors of the levels below, at, and above the barrier have also been observed.

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