We observed rotationally resolved spectra of A(0 +) ← X(0 +) and B(1) ← X(0 +) transition of PbO produced in a flow cell by laser ablation. The transition frequency was calibrated using an ultralow expansion etalon and (4s 2 S 1/2-5p 2 P 1/2) absorption line of K atoms at 405 nm within the error of 3 MHz. We determined the rotational constants for a number of vibrational levels of three isotopic molecules, 206 PbO, 207 PbO, and 208 PbO. The interaction among electronic excited states are generally significant in such heavy molecules, and we found perturbations in specific rotational levels [1]. We discuss the potential energy curves of low electronic excited states of PbO on the basis of the global analysis of observed transitions.

A continuous excitation band of a free-bound photoassociation transition of ytterbium atoms is observed as a red wing of the 1 S0 -1 P1 atomic line at 399 nm for a hot thermal vapor. The excitation to the 0 + u molecular state is observed by monitoring fluorescence from the 3 P1 state atoms, which allows us to detect the production of Yb 2 molecules with high sensitivity. The photoassociation is characterized in comparison with transitions to atomic Rydberg states. The time profile of the fluorescence signal suggests that the 0 + u molecular state predissociates with states correlating to the 1 S0 + 3 D2 atomic states.