Negative ions $\mathrm{Ar}^{-}$, $\mathrm{Kr}^{-}$, and $\mathrm{Xe}^{-}$ in superfluid helium

The catalogue of negative ions in superfluid helium has been extended using the example of $\mathrm{Ar}^{-}$, $\mathrm{Kr}^{-}$, and $\mathrm{Xe}^{-}$ . Such objects cannot exist in vacuum, since the polarization attraction of an electron to the inert $\mathrm{A}$ atom is insufficient for the formation of the bound state $\mathrm{A}^-$. However, these objects exist in helium as stable or metastable with a very long lifetime. The effect is due to the electron localization in liquid helium. If a mixture of excited $\mathrm{A}^*$ atoms and electrons is prepared in the gas phase above liquid helium, the reaction $\mathrm{A}^{*}+e=\mathrm{A}^{*-}$ becomes possible for all atoms of the periodic table. Such charges can be immersed into liquid helium by the electric field. In this case, the radiative decay $\mathrm{A}^{*-}=\mathrm{A}+e$ allowed in vacuum can be forbidden in liquid. This leads to the formation of the new unique objects $\mathrm{A}^-$, which can exist in liquid helium but are absent in nature. The size of such charged formations has been determined and is close the radius of a usual electron bubble in helium.