Ultrafast fragmentation and vibrational dynamics of triatomic hetero- and homonuclear alkali metal clusters

The one-color femtosecond pump and probe spectroscopical technique was empl oyed to study the fragmentation kinetics and vibration dynamics of the diss ociative excited states of alkali trimer clusters K2Na, K-3 and Na2K locate d in the spectral region between 730 and 840 MI. The electronically excited states were populated by a pump pulse via one-photon absorption. The tempo ral evolution of the excited state was then monitored by ionizing the parti cle at a variable delay with a two photon transition. The lifetimes of the predissociated excited states strongly depend on the excitation wavelengths : 2.8-5.1 ps for K2Na, 7.5-9.8 ps for K-3, and 2.5-5.8 ps for Na2K. Further more, the dominant fragmentation channels were identified as well. In the c ase of the Na2K trimer a clear wavepacket dynamics with an oscillation peri od of about 490 fs was observed at an excitation wavelength of 770 nm. In t he case of the K-3 and K2Na trimers, no pronounced oscillatory ion signal i ndicative of a vibrational dynamics was observed at the applied wavelength region.