ON THE METASTABILITY OF THE (1)SIGMA(G)(+) GROUND-STATE OF HE-2(2+) AND NE-2(2+) - A CASE-STUDY OF BINDING METAMORPHOSIS

The transition from stable to metastable and finally to unstable situations for increasing nuclear charge Z is studied in the adiabatic approximation for the 1SIGMA(g)+ ground state of homonuclear diatomic molecular systems with two or eighteen electrons. Allowing non-integer values for the parameter Z and varying it in small steps, critical values for stability Z(c) and metastability Z(m) are determined by means of extensive and accurate ab initio calculations. In addition, the behaviour of various other quantities (equilibrium distances, lowest bound or resonance levels of vibrational motion) is monitored during the transition. Our results confirm, in particular, the metastability of the He-2(2+) ground state, but exclude the possibility of a metastable 1SIGMA(g)+ state for the recently experimentally observed Ne2(2+).