Fast moving nuclei in Li19 clusters as evidenced by molecular beam ESR experiments

ESR spectra of free lithium clusters Li11 and Li19 were measured by a molecular beam method. The spectra show that the observed clusters are Li10 + Li and Li18 + Li, i.e., Li10 and Li18 with an atomic Li attached to them. The host cluster Li18 in Li19 is highly spin-polarized by the attached atom, and gives the spectrum a large number of equally spaced hyperfine-lines indicating 18 equivalent nuclei, which reveal fluid-like behavior of Li18 at an estimated internal temperature of T = 102 K. The host cluster Li10 in Li11 is only weakly spin-polarized probably because Li10 is an ordinary solid-like cluster.