ENERGY SHIFTS FOR A HELIUM ATOM NEAR ALUMINUM SURFACES

By consideration of the Bottcher model potential we obtain numerically the electrostatic energy shifts for the ground and some excited state s (n = 2, m = 0) of He in front of an Al surface. For the ground state , our electrostatic energy curve follows an image charge behavior 1/4d (where d represents the atom-surface distance in atomic units) even u p to distances d = 2, at which the energy shift is comparable in magni tude to the work function of Al. For the excited states which have a 1 /4d behavior only for d greater than or equal to 15, our electrostatic results are compared with earlier calculations which include simultan eously electrostatic and pure quantum contributions to the shift. From this we infer that the (always upward) electrostatic shift is much la rger than the pure quantum shift when d greater than or equal to 10 fo r the 2S states and when d greater than or equal to 8 for the 2P state s, although in the region 5 < d < 8 is the pure quantum contribution w hich induces the large upward shift of the 2S state and the downward s hift of the 2P state which causes the attraction of these levels. (C) 1998 Elsevier Science B.V. All rights reserved.