Spectroscopy and perturbation analysis of the A¹π (v=0) state of ¹³ C¹⁶ O

The lowest v = 0 level of the A¹Π state of the ¹³C¹⁶O isotopologue of carbon monoxide has been reinvestigated with a variety of high-resolution spectroscopic techniques. The A¹Π −X¹Σ⁺(0, 0) band has been studied by vacuum-ultraviolet Fourier-transform absorption spectroscopy, using the SOLEIL synchrotron as a radiation source. Spectra were obtained under quasi-static gas conditions at liquid-nitrogen temperature, room temperature and at an elevated temperature of 900 K, with absolute accuracies of 0.01−0.03 cm⁻¹. Two-photon Doppler-free laser spectroscopy has been applied to a limited number of transitions in the A¹Π −X¹Σ⁺(0, 0) band, under collision-free circumstances of a molecular beam, yielding an absolute accuracy of 0.002 cm⁻¹. The third technique is high-resolution Fourier-transform emission spectroscopy in the visible region applied to the B¹Σ⁺ −A¹Π(0, 0) band in a gas discharge, at an absolute accuracy of up to 0.003 cm⁻¹. With these methods, rotational levels of A¹Π (0) could be studied in both parity components up to a rotational quantum number of J = 46. The frequencies of 397 transitions were used to analyse the perturbations between the A¹Π(0) level by vibrational levels of the D¹Δ, e³Σ⁻, d³Δ, and a′³Σ⁺ states.