High-resolution spectroscopy of the X 0⁺→ A0⁺, C0⁺ transitions of PbO in 22 300–25 100 cm^-1

High-resolution excitation spectra of the X0⁺→ A0⁺ and X0⁺→ C0⁺ transitions of lead monoxide (PbO) are observed in a range of 22 300-25 100 cm⁻¹. Transition frequencies are determined with an average uncertainty of 8.5×10⁻⁴ cm⁻¹ by comparing with resonances of an ultralow expansion etalon. PbO molecules are produced by laser ablation in a cold helium buffer gas, which provides rotationally cold but vibrationally hot molecules and allows observation of hot bands of excitation from the υ^′′=1,2 vibrational states. Spectroscopic constants and potential curves for the A0⁺ and C0⁺ states are determined, and the spectroscopic constants obtained for the three main isotopologues are reproduced to a satisfactory level using a single potential curve for each electronic state. This indicates that perturbation due to other electronic states is negligibly small.