DIABATIC REPRESENTATIONS OF THE EXCITED ${^{1}\Sigma_{g}}^{+}$ STATES OF MOLECULAR HYDROGEN.

$^{1}$K. Dressler, K. Gallusser, P. Quadrelli, and L. Wolniewicz, J. Mol. Spectrosc. 75, 205 (1979); K. Dressler and L. Wolniewicz, J. Mol. Spectrosc. 86, 534 (1981); and unpublished results.Ab initio calculations on the lowest three excited ${^{1}\Sigma_{g}}^{+}$ states of molecular hydrogen, EF, GK, and $H\bar{H}$, performed on the basis of adiabatic electronic stated, have provided wavefunctions, energies, and non-adiabatic nuclear dynamical coupling $functions.^{1}$ This basis can be transformed into an infinite number of diabatic bases consistent with the ab-initio nuclear dynamical coupling functions. Any one of these diabatic representations is suitable for solving the coupled vibrational equations, but the most interesting and useful diabatic basis would be one containing states with pure Rydberg or pure non-Rydberg character, such that the knowledge of the lowest members of Rydberg series and of their Rydberg-valence interactions would permit predictions of the properties of the whole Rydberg series and of the adjoining ionisation continua. The corresponding ab-initio computations on the higher series members in the adiabatic basis would be extremely laborious