Session K7 - Chemical Dynamics at Surfaces II.
MIXED session, Wednesday afternoon, March 19
Room 4202A, Conv. Center
The quartet states of Na_3 and K_3 form when three alkali atoms with parallel electron spins collide with, and are picked up by a beam of large liquid He clusters. Laser induced fluorescence excitation and emission spectra of the 2^4E'-1^4A_2' electronic transition of Na_3 reveal a non-adiabatic surface crossing of the quartet trimer into the doublet manifold. Three channels of fluorescence are observed. In addition to the direct emission to the lowest quartet state, fluorescence from the dissociation products is emitted at higher energies than the excitation photons, as chemical energy is converted to electronic energy. Vibrational analysis of the emission to the lowest quartet state is used to test the validity of a potential surface calculated at the CCSD(T) level. The potential surface reveals an 80% three-body contribution to the binding energy at the equilibrium geometry of the trimer. A contraction of the Na-Na bond distance from 5.09 Åin the triplet dimer to 4.4 Åin the trimer is observed. This paper is dedicated to the memory of J. A. Barker who pioneered the study of three-body forces in molecular systems.