FT-spectroscopy of the CO rare isotopologue and deperturbation analysis of the AΠ(v = 3) level.

Research on CO was carried out using two complementary Fourier-transform methods: (1) vacuum-ultraviolet absorption spectroscopy, with an accuracy ca. 0.03 cm on the DESIRS beamline (SOLEIL synchrotron) and (2) visible emission spectroscopy with an accuracy of about 0.005-0.007 cm by means of the Bruker IFS 125HR spectrometer (University of Rzeszów). The maximum rotational quantum number of the energy levels involved in the observed spectral lines was J = 54. An effective Hamiltonian and the term-value fitting approach were implemented for the precise analysis of the AΠ(v = 3) level in CO. It was performed by means of the PGOPHER code. The data set consisted of 571 spectral lines belonging to the AΠ-XΣ(3, 0), BΣ-AΠ(0, 3), CΣ-AΠ(0, 3) bands and several lines involving states that perturb the AΠ(v = 3) level as well as to the previously analysed BΣ-XΣ(0, 0) and CΣ-XΣ(0, 0) transitions. A significantly extended quantum-mechanical description of the AΠ(v = 3) level in CO was provided. It consists of the 5 new unimolecular interactions of the spin-orbit and rotation-electronic nature, which had not been taken into account previously in the literature. The ro-vibronic term values of the AΠ(v = 3, J = 55), a'Σ(v = 13), DΔ(v = 4) and IΣ(v = 5) levels were determined with precision improved by a factor of 10 relative to the previously known values.