Perturbations in the A¹Π, <i>v</i> = 0 state of ¹²C¹⁸O investigated via complementary spectroscopic techniques

The A¹Π(<i>v</i> = 0) level of ¹²C¹⁸O has been reinvestigated using three different high-resolution spectroscopic methods: (1) 2 + 1′ resonance-enhanced multiphoton ionisation of the A¹Π − X¹Σ⁺(0, 0) band using narrowband lasers in a Doppler-free geometry; (2) Fourier-transform emission spectroscopy in the visible range probing the B¹Σ⁺ − A¹Π(0, 0) band in a discharge; (3) Fourier-transform absorption spectroscopy in the vacuum-ultraviolet range measuring the A¹Π − X¹Σ⁺(0, 0) and B¹Σ⁺ − X¹Σ⁺(0, 0) bands at multiple temperatures ranging from 90 to 900 K. An effective-Hamiltonian analysis of A¹Π, <i>v</i> = 0 levels was performed up to <i>J</i> = 44 which quantitatively addresses perturbations by the e ³Σ⁻(<i>v</i> = 1), d³Δ(<i>v</i> = 4), a′³Σ⁺(<i>v</i> = 9), D ¹Δ(<i>v</i> = 0), and I ¹Σ⁻(<i>v</i> = 0, 1) levels.