Optical spectra of metal dimers and trimers in superfluid helium

Electronic spectra of ${\mathrm{Ca}}_2$, ${\mathrm{Cu}}_2$, and ${\mathrm{Ag}}_3$ have been studied in superfluid helium. The Σ-Σ transitions of ${\mathrm{Ca}}_2$ and ${\mathrm{Cu}}_2$ show vibrationally resolved absorption and emission bands close to those in free space. The emission has been observed only from the lowest vibrational states, reflecting rapid relaxation of the dimer vibration. Vibrational frequencies of the ground electronic states are slightly affected by the liquid. Anomalous spacings between the v′=0←v′′=0 and v′=1←v′′=0 absorption bands are discussed in terms of the coupling of dimer vibration and bubble bath modes.