DISPERSED FLUORESCENCE STUDIES OF QUARTET STATE ALKALI TRIMERS

Author Institution: Department of Chemistry, Princeton University; Fakult\'{a}t f\""{u}r Physik, Universit\""{a}t Bielefeld, Universit\""{a}tsstr; Department of Chemistry, University of Gd\'{a}nskThe high spin states of $Na_{3}$ and $K_{3}$ 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 $2^{4}E^{\prime} - 1^{4}A_{2}^{\prime}$ transition of $Na_{3}$ 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 $Na_{3}$ and $K_{3}$: a) direct emission to the lowest quartet state of the trimer, b) $n^{2}P_{3/2, 1/2} - n^{2}S_{1/2}$ atomic fluorescence, and c) fluorescence from the singlet dimer (B) $1^{1}\Pi_{u}-(X)1^{1}\Sigma^{+}_{g}$ 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 $Na_{3}$ 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