Experimental Study of Highly Excited ¹Σ_g⁺ and ¹Π_g States of the Cesium Dimer

We report the results of an experimental study on the highly excited 11 ¹Σ_g⁺ and 6 ¹Π_g electronic states of the cesium dimer. The rovibrational structure of these states was probed using the optical-optical double resonance (OODR) technique in which Cs₂ molecules from thermally populated levels in the X ¹Σ_g⁺ ground state were excited through intermediate levels in either the B¹Π_u state or the mixed A¹Σ_u⁺ ∼ b³Π_u manifold. The probe laser resonance frequencies were determined by detecting laser induced fluorescence (LIF) from the target states to the a³Σ_u⁺ triplet ground state. The observed states were identified as ¹Σ_g⁺ and ¹Π_g electronic states based on the selection rules for dipole allowed transitions followed by the line patterns in the recorded excitation spectra. Bound-bound fluorescence spectra from rovibrational levels in the target states down to the A ∼ b manifold were also taken to further confirm electronic state multiplicity. Two sets of Dunham coefficients corresponding to the two target states were fitted from experimentally determined term values and are reported in the present work. Potential energy curves constructed from these Dunham coefficients are also presented and compared to ab initio curves from our collaborators.