Electronic and vibronic structure ofLi4observed by depletion spectroscopy

We report the observation of electronically excited states of ${\mathrm{Li}}_4$, using depletion spectroscopy. The obtained spectra reveal five electronic bands between 380 and 760 nm. Energetic locations and absorption cross sections (ranging from 0.3 to 4 Å ${}_{}{}^2{}_{}{}^{}$) fully agree with previous molecular configuration-interaction ab initio calculations. Vibronic structures are also observed; they look promising for development of accessibility to adiabatic surfaces and equilibrium geometries in metallic tetramers.