Observation of the K2 43Δg state by cw perturbation-facilitated optical–optical double resonance spectroscopy

This paper reports for the first time both, an experimental observation and theoretical calculations of the K 2 4 3 Δ g state. For the experiment we used cw perturbation-facilitated optical–optical double resonance (PFOODR) spectroscopy. A single mode Ti-sapphire laser and a dye laser served as the pump and probe lasers, respectively. A total of 55 PFOODR signals have been assigned to the 4 3 Δ g ← b 3 Π u transitions. Absolute vibrational numbering was determined by using quantum defect analysis combined with comparing observed intensities with calculated Franck–Condon factors (FCF). For the former we used known parameters from the 2 3 Δ g state since the 2 3 Δ g and the 4 3 Δ g states belong to the same Rydberg series. We report here our experimental and calculated spectroscopic constants, the corresponding RKR potential energy curve, the Franck–Condon table for the 4 3 Δ g ↔ b 3 Π u system, as well as a comparison with the theoretical potential energy curve. The T e value is found to be 28408.938(52) cm −1 .