Knowledge Bank

The high spin states of $Na3$ and $K3$ can be formed on the surface of large helium clusters by the aggregation of three alkali atoms with parallel electron spins. The emission spectrum of the $24E\prime -14A2\prime$ transition of $Na3$ reveals that a non-adiabatic spin flip process occurs in the excited state that leads to an intersystem corssing into the doublet manifold of the trimer. A total of three channels of fluorescence are observed in both $Na3$ and $K3$: a) direct emission to the lowest quartet state of the trimer, b) $n2P3/2,1/2-n2S1/2$ atomic fluorescence, and c) fluorescence from the singlet dimer (B) $11\Pi u-(X)11\Sigma g+$ transition. The latter two correspond to the emission of the dissociation products of the doublet trimer after curve crossing. Vibrational analysis of the lowest quartet state of $Na3$ provides spectroscopic data with which to test ab-initio potential surfaces. The study of the quartet state trimars provides information on the three-body component of the intermolecular energy in these van der Waals molecules. The possibility for time resolved dynamical studies of this simple unimolecular reaction will also be discussed.