High-resolution Fourier-transform spectroscopy and deperturbation analysis of the A¹Π(v = 1) level in ¹²C¹⁸O

The A¹Π(v = 1) level of the ¹²C¹⁸O isotopologue was precisely reinvestigated with two complementary spectroscopic techniques. High resolution B¹Σ⁺ → A¹Π(0, 1), (1, 1) and C¹Σ⁺ → A¹Π(0, 1) emission bands were recorded in the visible region, 20,700 – 26,100 cm⁻¹, with a 1.71 m Fourier-transform spectrometer (Bruker IFS 125-HR) installed at the University of Rzeszów. The resulting line centre accuracy of isolated and medium to strong lines is 0.005 cm⁻¹. In addition, high-resolution spectra of the A¹Π ⟵ X¹Σ⁺(1, 0), B¹Σ⁺⟵ X¹Σ⁺(0, 0) and (1, 0) as well as C¹Σ⁺⟵ X¹Σ⁺(0, 0) bands were recorded between 66,200 and 95,250 cm⁻¹ using the vacuum-ultraviolet Fourier-transform spectrometer installed at the DESIRS beamline of the SOLEIL synchrotron. The wavenumber accuracy for isolated and strong spectral lines is 0.01 cm⁻¹. A data set of 626 spectral lines belonging to seven bands was incorporated into a global deperturbation analysis. Significantly improved deperturbed molecular constants for the A¹Π(v = 1), a´³Σ⁺(v = 10), D¹Δ(v = 1), and I¹Σ⁻(v = 2) levels, term values of the B¹Σ⁺(v = 0, 1) and C¹Σ⁺(v = 0) Rydberg states as well as the accompanying spin-orbit and rotation-electronic (L-uncoupling) interaction parameters were obtained. The experimental ro-vibrational term values of the A¹Π(v = 1) level and its perturbers were also determined. The mixed composition of interacting states is expressed in terms of their ¹Π percentage character.