Optimal double-configuration study of the lowest excited Π states of H₂ - II. σ - π separation

The σ - π separation of energies and one-electron properties of the four lowestlying Π states of the hydrogen molecule considered in the preceding paper [1] is presented. The calculations are based on separate exponent optimization for all four states. The values of the σ electron properties of the four states are much closer than those of the π electrons. The degree of uniformity of the π electron property values increases when a lesser level of approximation based on a single-state (1Πu) exponent set is used. The assumption of equal parameter values for different states in semiempirical π electron methods is valid only on this level. Conclusions based on this assumption cannot lead us to a representative description of the antibonding character of molecular states. © 1972 Springer-Verlag.