VUV-VIS FT spectroscopy of the rare CO isotopologue of carbon monoxide: Analysis of the AΠ(v = 1) multiply-perturbed level.

Ro-vibronic spectra of the CO carbon monoxide isotopologue were obtained with (i) emission spectroscopy in the visible region using a Bruker IFS 125HR spectrometer (University of Rzeszów) and (ii) vacuum-ultraviolet absorption spectroscopy using the wave-front-division spectrometer on the DESIRS beamline of the SOLEIL synchrotron. A deperturbation analysis of the CO AΠ(v = 1) level was conducted from 598 observed transitions from the BΣ - AΠ(0, 1), CΣ - AΠ(0, 1), AΠ - XΣ(1, 0), BΣ - XΣ(0, 0), CΣ - XΣ(0, 0), IΣ - XΣ(2, 0) bands and five further nominally forbidden bands. An effective Hamiltonian and term-value fitting analysis was implemented. Consequently, 135 parameters were floated: 23 molecular parameters, including molecular constants for AΠ(v = 1), IΣ(v = 2), dΔ(v = 6), eΣ(v = 3) and DΔ(v = 1); rotation-electronic (L-uncoupling) mixing of AΠ(v = 1) ∼ [DΔ(v = 1), IΣ(v = 1), IΣ(v = 2)] and spin-orbit interaction parameters for AΠ(v = 1) ∼ [dΔ(v = 6), eΣ(v = 3), a'Σ(v = 11)]; the spin-orbit/spin-electronic/L-uncoupling aΠ(v = 12) ∼ dΔ(v = 5) and spin-orbit aΠ(v = 12) ∼ [DΔ(v = 1), IΣ(v = 2)] perturbation parameters; as well as 112 ro-vibronic term values of BΣ(v = 0) up to J = 50 and CΣ(v = 0) up to J = 60. The significant, indirect aΠ(v = 12) ∼ [eΣ(v = 2, 3), dΔ(v = 5, 6)] ∼ AΠ(v = 1) spin-orbit/spin-electronic/L-uncoupling interaction and aΠ(v = 12) ∼ [IΣ(v = 2), DΔ(v = 1)] ∼ AΠ(v = 1) spin-orbit/L-uncoupling interaction were detected and analysed. Thus, this study, using modern experimental methods and deperturbation analysis, leads to a much improved description in terms of molecular constants and interaction parameters, compared to previous studies of the AΠ(v = 1) energy region in the CO isotopologue. This research is a continuation of the studies on the AΠ state and its numerous perturbers in the CO isotopologues made by our team.