The C${}^1{\mathrm{\Pi }}_{\mathrm{u}}$ state of potassium dimer revisited: an~extensive study by polarisation labelling spectroscopy method

The polarisation labelling spectroscopy technique was applied to study the C${}^1{\mathrm{\Pi }}_{\mathrm{u}}$ $\leftarrow$ X${}^1{\mathrm{\Sigma }}_{\mathrm{g}}^{+}$ band system in potassium dimer. About 1100 new rotationally resolved molecular lines were measured in the $22100-24100$~cm${}^{-1}$ spectral range. Perturbations of the lowest vibrational levels of the C state were localised and their origin discussed. A set of Dunham coefficients was deduced to fit the unperturbed levels of the C${}^1{\mathrm{\Pi }}_{\mathrm{u}}$ state with $0\le v\le 38$ and $18\le J\le 101$ and the potential energy curve of the state was constructed.