On the 3$^{1}\Pi_{u}$ state in caesium dimer.

Polarisation labelling spectroscopy technique was employed to study the 3$^{1}\Pi_{u}$ state of Cs$_2$ molecule. The main equlibrium constants are $T_e=20684.60$cm$^{-1}$, $\omega_e=30.61$cm$^{-1}$ and $R_e=5.27$\r{A}. Vibrational levels $v=4-35$ of the 3$^{1}\Pi_{u}$ state were found to be subject to strong perturbations by the neighbouring electronic states. Energies of 3094 rovibronic levels of the perturbed complex were determined.