Negative ions in liquid helium

The structure of negative ions in liquid (4)He is analyzed. The possibility of cluster or bubble formation around impurity ions of both signs is discussed. It is shown that in superfluid helium, bubbles form around negative alkaline earth metal ions and clusters form around halogen ions. The nature of fast and exotic negative ions is also discussed. It is assumed that fast ions are negative ions of helium excimer molecules localized inside bubbles. Exotic ions are stable negative impurity ions, which are always present in small amounts in gas discharge plasmas. Bubbles or clusters with radii smaller the radius of electron bubbles develop around these ions. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3599656]