A configurational study of helium clusters doped with He^∗− and He₂^∗−

Helium clusters doped with electronically excited atomic and molecular helium anions He^∗− and He₂^∗− at T = 0.4 K are studied by means of path integral Monte Carlo calculations. Geometry and energetics of the systems with up to 32 solvating He atoms are characterised. The interactions between the anions and the neutral He atoms have been described by fitting previously reported ab initio points to analytical expressions. The He_N–He^∗− clusters with N > 6 display a structure defined by a bipyramid which completely solvates the atomic anion, whereas the rest of surrounding He atoms form a dimple around that initial cage. On the contrary, the structures observed for the He_N–He₂^∗− clusters clearly show the dopant located outside the helium droplet, thereby confirming the heliophobic character of He₂^∗−