Undulations of the potential-energy curves for highly excited electronic states in diatomic molecules related to the atomic orbital undulations

We present potential-energy curves for highly excited electronic states of diatomic molecules showing spectacular undulations including multiple barriers and wells. Those undulations unrelated to avoided crossings are closely correlated with the oscillations of atomic radial electron density in the Rydberg States. The LiHe, LiNe, and LiH cases are examined with an accurate quantum chemical calculation, For the Sigma(+) states originating from the ns, np, nd, or nf states of lithium atom, n-2 potential barriers and the same number of potential wells exist. The 4 (1)Sigma(g)(+)(F) state-of Li-2 also shows the energy barrier of the same origin, This spectroscopic property is supposed to be more general in diatomic molecules and other small molecules. [S1050-2937(99)08202-5].