Ultrafast Fragmentation and Vibrational Dynamics of Triatomic Hetero‐ and Homonuclear Alkali Metal Clusters

The one‐color femtosecond pump and probe spectroscopical technique was employed to study the fragmentation kinetics and vibration dynamics of the dissociative excited states of alkali trimer clusters K 2 Na, K 3 and Na 2 K located in the spectral region between 730 and 840 nm. The electronically excited states were populated by a pump pulse via one‐photon absorption. The temporal evolution of the excited state was then monitored by ionizing the particle 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 K 2 Na, 7.5‐9.8 ps for K 3 , and 2.5‐5.8 ps for Na 2 K. Furthermore, the dominant fragmentation channels were identified as well. In the case of the Na 2 K trimer a clear wavepacket dynamics with an oscillation period of about 490 fs was observed at an excitation wavelength of 770 nm. In the case of the K 3 and K 2 Na trimers, no pronounced oscillatory ion signal indicative of a vibrational dynamics was observed at the applied wavelength region.