Formation of solid helium-rings surrounding Mg and Be atoms in liquid helium

Summary form only given. Laser-induced fluorescence (LIF) studies of impurity atoms dispersed in liquid helium have provided much insight into the microscopic structure of helium atoms surrounding the impurities. For example, a largely red-shifted and broadened emission spectrum of Ag atoms in liquid helium has been attributed to the formation of AgHe₂ exciplexes. On the other hand, heavy members of the group IIA atoms (Ca, Sr, and Ba) are known not to form metal-He_n exciplexes in their lowest singlet P-states. The lowest singlet emissions of those atoms show only small shifts and broadening and have been semi-quantitatively explained by the so called bubble model. However, we found that Mg and Be, the two lightest members of group IIA atoms, show quite anomalous LIF spectra in liquid helium. The experiments were performed in a metal Dewar equipped with quartz windows. Mg and Be atoms were dispersed into liquid helium at ~1.6 K by a laser ablation and dissociation method, and excited by a pulsed dye laser beam. Dispersed LIF was detected by a photomultiplier followed by a boxcar integrator