Highly excited 3Πg electronic states of the cesium dimer— Ab initio predictions and experimental observation of the 63Πg state

We report the results of an experimental investigation of the highly excited 6Πg3 electronic state of the Cs2 molecule. In addition, we present ab initio potential energy curves for all Cs2Πg3 electronic states up to the 6s+7d limit, calculated using the pseudopotential method. Rovibrational levels of the excited triplet state were observed experimentally using the perturbation facilitated optical–optical double resonance technique, with levels of the AΣu+1∼bΠu3 mixed manifold serving as intermediate states. A progression of P and R branch probe laser resonances was detected by measuring laser-induced fluorescence to the aΣu+3 state as a function of the probe laser frequency. For select rovibrational levels of the 6Πg3 state, dispersed fluorescence to the aΣu+3 state and the AΣu+1∼bΠu3 manifold was recorded and compared with Franck–Condon factor calculations to determine the state multiplicity and vibrational numbering. Using the electric dipole selection rules and comparison with our ab initio results allowed the experimentally observed levels to be assigned to the 6Πg3 state. Term values of the 270 observed rovibrational levels of the 6Πg3 state were fit to a Dunham expansion. From the fitted Dunham constants, a potential energy curve was constructed using the Rydberg–Klein–Rees method.