The characterization of supersonic sodium vapor expansions including laser induced atomic fluorescence from trimeric sodium

Abstract

A supersonic expansion of pure sodium metal has been used to form small sodium clusters Mn, n⩾2. Discussion focuses on the characterization of variously produced sodium supersonic expansions and the analysis of laser induced atomic fluorescence (LIAF) resulting from the photodissociation of triatomic sodium clusters. We consider: (1) the nature of observed ’’fluctuation’’ bands corresponding to the pumping of bound-free transitions which yield P2 (Na D-line) sodium atoms and ground state Σg+1, Na2 and the distinctly different spectral characteristics associated with these bound-free transitions as they are observed in either high purity of highly disrupted supersonic expansion; (2) the possibility of controlled ’’hot band’’ formation through disruption of the free jet expansion, allowing the mapping of vibronic structure in the ground electronic and low-lying electronic states of the weakly bound sodium trimer molecule; (3) the determination of an upper bound Do⩽4250 cm−1 for the Na–Na2 bond energy from the analysis of the sodium trimer LIAF spectrum obtained in high purity expansion; and (4) the observation of very efficient energy transfer between sodium dimer and polyatomic sodium. The current studies are discussed in the light of recent experimental and theoretical characterization of bound–bound transitions in Na3, and the possible application of LIAF to the study of bound-free transitions in other small metal clusters is considered.