Experimental characterisation of the double minimum 61Σ+ state in NaRb

Polarisation labelling spectroscopy technique was employed to study the double minimum 61Σ+ state of NaRb molecule. Six lines of an argon ion laser were used to label rovibronic levels in the electronic ground state and the excitation spectra in the 61Σ+ ← X1Σ+ band system were recorded in the spectral range 24 100–26 500 cm−1. Energies of 901 rovibronic levels of the inner well of the 61Σ+ state were determined for two isotopomers of NaRb. The potential curve of the 61Σ+ state was constructed using the inverted perturbation approach method.