Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4

Abstract

We have observed several new spectral features in the fluorescence of cesium atoms implanted in the hcp phase of solid helium following laser excitation to the 6${}^2$P states. Based on calculations of the emission spectra using semiempirical Cs-He pair potentials the newly discovered lines can be assigned to the decay of specific Cs*He${}_n$ exciplexes: an apple-shaped Cs$(A{\Pi }_{3/2})$He${}_2$ and a dumbbell-shaped Cs$(A{\Pi }_{1/2})$He${}_n$ exciplex with a well defined number $n$ of bound helium atoms. While the former has been observed in other enviroments, it was commonly believed that exciplexes with $n>2$ might not exist. The calculations suggest Cs$(A{\Pi }_{1/2})$He${}_6$ to be the most probable candidate for that exciplex, in which the helium atoms are arranged on a ring around the waist of the dumbbell shaped electronic density distribution of the cesium atom.

4 pages, 4 figures