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

The A1Π(v = 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, v = 0 levels was performed up to J = 44 which quantitatively addresses perturbations by the e 3Σ−(v = 1), d3Δ(v = 4), a′3Σ+(v = 9), D 1Δ(v = 0), and I 1Σ−(v = 0, 1) levels.