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.