Experimental study of the 3¹Δ_g and 4¹Δ_g states of Rb₂

We report a high-resolution experimental study of the highly excited 3¹Δ_g and 4¹Δ_g electronic states of the ⁸⁵Rb₂ dimer. Rovibrational levels of the two electronic states were probed using the optical-optical double resonance (OODR) technique by exciting ⁸⁵Rb₂ molecules from thermally populated levels of the X¹Σ_g⁺ ground state through intermediate levels of the B¹Π_u electronic state. The resonances of the probe laser were observed by detecting the laser induced fluorescence (LIF) from the target states to the a³Σ_u⁺ triplet ground state. The ¹Δ_g character of the two electronic states was confirmed by showing that the transitions to these states abide by ¹Π - ¹Δ dipole selection rules and by observing that their lowest rotational level is J = 2. Preliminary molecular constants and Rydberg-Klein-Rees (RKR) potential energy curves from the observed term values were calculated for each electronic state and compared with ab initio calculations.