On the use of liquid helium cluster beams for the preparation and spectroscopy of the triplet states of alkali dimers and other weakly bound complexes

Sodium dimers in their lowest triplet state are prepared by pick-up of sodium atoms by a beam of large (n≂104) liquid helium clusters when these cross a scattering box containing sodium vapor. Using laser induced fluorescence detection the vibrationally resolved laser excitation spectrum of the 1 3Σ+g←1 3Σ+u transitions of Na2 is obtained. The spectral shifts with respect to the corresponding gas phase values are surprisingly small. These data show the feasibility of using helium clusters as an almost ideal matrix for the synthesis and spectroscopic analysis of weakly bound complexes.