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Using Infrared-Infrared Double Resonance (IIDR) high resolution spectroscopy, we have observed the 20 200–21 600 cm−1 energy range of the 4 1 Σ g + electronic state of Rb 2 . The absolute vibrational quantum number assignment is based on the isotope effect using 824 rovibrational levels assigned to the 85 Rb 85 Rb and 85 Rb 87 Rb isotopomers. In addition to perturbations between the 4 1 Σ g + and 3 1 Σ g + state, strong couplings between the 4 1 Σ g + and 2 3 Π g states were observed. Preliminary molecular constants and an RKR potential energy curve are given.

Electromagnetically induced transparency has been observed in 39 K 2 two-photon transitions by fluorescence detection. The two-photon absorptions correspond to 2 3 Π g ← X 1 Σ g + transitions through A 1 Σ u + ∼ b 3 Π u mixed intermediate enhancing levels, which are coincidentally on resonance with the excitation laser frequency. Laser intensity dependence of this effect has been studied and different detection schemes have been applied.

This Letter reports on state to state collision energy transfer in the A1Σu+ and G(2)1πg states of both 7Li2 and 6Li7Li dimers. The molecules were electronically excited by a single laser excitation or by using optical-optical double resonance (OODR) technique. Either a fluorescence or an ionization signal was monitored. A breakdown of the symmetric antisymmetric (s ⇎ a) rotational level selection rule was observed for collisional transitions in the A1Σu+ state of th nearly homonuclear 6Li7Li molecule. However, no s ⇎ a radiative transition breakdown was detected when we attempted the X1Σg+ → A1Σu+ → C(1)1πg ungerade-ungerade electronic excitation. Propensities for rotational energy transfer in the G(2)1πg state are discussed.

Collisional energy transfer between 1 Δ g and 1 Σ + g Rydberg states of K 2 has been studied by optical-optical double resonance (OODR) resolved fluorescence spectroscopy. The collision-induced probability for transition from a 1 Δ g state to an adjacent 1 Σ + g state of K 2 depends much more strongly on Δ J than on Δ E in each case studied. Δ J = 0 collision transfer is more favorable than Δ J = ±2, … for 1 Δ g odd J e levels. For 1 Δ g even J f levels, Δ J = ± 1 transfers are most favorable. The measurements of intensities of 1 Δ g , 1 Σ + g ← B 1 Π u , υ′ = 2, J ′ = 14e transitions and fluorescence intensities show that the collision-induced transition probability of these 1 Δ g - 1 Σ + g systems is quite large.

A UV Ar 2+ laser was used to excite specific levels in the C 1 Π u state of the 7 Li 2 dimer. A subsequent photochemical reaction with atomic Mg produced the LiMg excimer in excited C 2 Π and D 2 Σ + states. The observed bound-free excimer emission spectrum was compared with theoretical emission profiles based on potential energy curves and transition dipole moments obtained from ab initio calculation. These calculations also indicate avoided crossings between the A 2 Π and C 2 Π states, and B 2 Σ + and D 2 Σ + states of LiMg.

We have used the experimental energy levels of the B state of Na2 to determine the shape of the potential curve. The potential curve obtained has been used to determine the Franck—Condon overlap of the continuum vibrational levels in the B state with bound levels in the ground electronic state.