Alkali Atoms

Yoshihiro Kubota, Yasushi Kino

In order to investigate the binding mechanism of weakly bound states of positronic alkali atoms, we calculate the energies and wavefunctions using the Gaussian expansion method (GEM) where a positronium (Ps)–alkali ion channel and a positron–alkali atom channel are explicitly introduced. The energies of the bound states are updated using a model potential that reproduces well the observed energy levels of alkali atoms. The binding mechanism of the positronic alkali atom is analyzed by the wavefunctions obtained. The structure of the positronic alkali atom has been regarded as a Ps cluster orbiting the alkali ion, which is described by the Ps–alkali ion channel. We point out that the fraction having the positron–alkali atom configuration is small but plays an indispensable role for the weakly bound system.

Galina Nemova

A. Hatakeyama, Katsunari Enomoto, T. Yabuzaki

Properties of alkali atoms (mainly rubidium and cesium) in a cold helium gas have been extensively studied. Experiments are performed at temperatures down to 1.2 K using alkali-metal vapor cells containing a helium buffer gas, with alkali atoms driven from the cell walls by one of three loading methods: laser ablation, light-induced atom desorption, and spark discharge. For alkali atoms loaded into the cold helium gas, we have found that the relaxation time of the electronic spin of optically polarized rubidium atoms in the ground state is about a minute, much longer than that achieved in conventional vapor cells at room temperature and above. We have also spectroscopically investigated the interactions of excited alkali atoms with helium atoms, especially the formation of alkali–He exciplexes.

Petar Stipanović, Leandra Vranješ Markić

Abstract Helium–alkali tetramers 4 He 3 A , 3 He 4 He 2 A and 3 He 2 4 HeA , where A is one of the alkali atoms 6,7 Li, 23 Na, 39,40,41 K, 85,87 Rb or 133 Cs, were studied using diffusion Monte Carlo method. Besides ground-state energies, exact distribution functions were evaluated. Spatial arrangements of atoms in clusters qualify He–A tetramers as transitional systems, which reveal halo-like spatial extension. On the one hand, swapping 4 He by 3 He atom in a He–Li tetramer, one can trace how quasi-halo structure transforms into halo structure. On the other hand, swapping 3 He by 4 He in He–A tetramer reveals behavior previously noticed in helium droplets doped with an alkali atom. Helium atoms start grouping on one side of an alkali atom, which is clearer in He–A clusters with more 4 He atoms that have stronger self-binding. The effect is the more pronounced the bigger alkali atom is, since it is then harder for the remaining He atoms to surround an alkali.