Dynamics of the 13Πg state of K2 on helium nanodroplets
Abstract
Fluorescence following optical excitation of the 13Σu+ state of K2 prepared on helium nanodroplets to the predissociative 13Πg state yields molecular emission from both the (B)11Πu and (A)11Σu+ K2 states as well as atomic emission from the expected 42P3/2,1/2 → 42S1/2 dissociation channel. A ∽12 cm−1 red shift is observed in the molecular emission excitation spectrum compared to the atomic emission excitation spectrum. Time-correlated photon counting measurements demonstrate the rise time for both atomic and molecular products to be <80 ps, independent of vibrational level excited. This lifetime is interpreted as the total depopulation time for the optically excited 13Πg state, which is dominated by intersystem crossing at low vibrational energy and by predissociation at the highest vibrational level. It is deduced that the timescale for intersystem crossing must be of the order of 10 ps. Symmetry restrictions for the isolated K2 imply that the intersystem crossing from the 13Πg state to the (B)11Πu and (A)1 1Σu+ states must be induced by interaction with the helium nanodroplet.