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