Femtosecond wave packet propagation dynamics in the dissociative K3 molecule

The potassium trimerʹs excited electronic state between 750 and 830 nm is predicted by theoretical calculations but could never be detected by continuous wave (cw) spectroscopic techniques. This state is now observed for the first time by femtosecond real-time three photon ionization (3PI). At an excitation wavelength of 798 nm the recorded temporal evolution of the one color 3PI signal presents an oscillatory structure with a dominant period of ∼ 450 fs which reflects the dynamics of the prepared wave packet. Fourier analysis reveals three frequencies (66, 82, 109 cm−1) which we interpret as normal modes of the trimerʹs ground and excited state. A superimposed decay (4−7 ps) is observed and reveals a rapid depopulation caused by ultrafast photodissociation.