OPTICAL-SPECTRA OF METAL DIMERS AND TRIMERS IN SUPERFLUID-HELIUM

Electronic spectra of Ca-2, Cu-2, and Ag-3 have been studied in superf luid helium. The Sigma-Sigma transitions of Ca-2 and Cu-2 show vibrati onally resolved absorption and emission bands close to those in free s pace. The emission has been observed only from the lowest vibrational states, reflecting rapid relaxation of the dimer vibration. Vibrationa l frequencies of the ground electronic states are slightly affected by the liquid. Anomalous spacings between the upsilon' = 0 <-- upsilon ' ' = 0 and upsilon' = 1 <-- v '' = 0 absorption bands are discussed in terms of the coupling of dimer vibration and bubble bath modes.