Photoinduced nonadiabatic dynamics in quartet Na3 and K3 formed using helium nanodroplet isolation

Helium nanodroplet isolation is used to produce van der Waals-bound quartet state alkali trimers ~Na3 and K3! selectively over the corresponding chemically bound doublet trimers. Frequency-resolved excitation and emission spectroscopy reveals the presence of nonadiabatic spin–flip processes in the electronically excited states. A total of four quartet to quartet electronic transitions are observed: the 2 E8,1 4E←1 A28 transitions of Na3 and the 1 A19,2 4E8←1 A28 transitions of K3 . Time-resolved spectroscopy reveals that intersystem crossing times in Na3 decrease from 1.4 ns after excitation of the 0–0 band to approximately 400 ps for the higher vibronic levels ~3,5/2!. Analysis of the resonant quartet fluorescence reveals that the excited electronic state cools vibrationally on a time scale that is comparable to, but slower than, the intersystem crossing time. © 2001 American Institute of Physics. @DOI: 10.1063/1.1418248#