PNNL

Abstract

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 non-adiabatic spin flip processes in the electronically excited states. A total of four quartet to quartet electronic transitions are observed: the 24E*,14E *14A2* transitions of Na3 and the 14A1**,24E**14A2* 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 timescale that is comparable with, but slower than the intersystem crossing time.