ADIABATIC AND QUASIDIABATIC 2-SIGMA+ STATES OF BEH

An approach to the calculation of quasidiabatic states is presented and applied to the rather entangled spectrum of the first five BeH 2SIGMA+ excited states. The method of transformation from the adiabatic to the diabatic description employs a criterion of maximum nonorthonormal overlap between sequential diabatic states along the coordinate of interest, starting with the dissociation region as a reference point. The computational method is general and capable of separating out diabatic states from a set of adiabatic ones of mixed character, involving valence, Rydberg and ion-pair contributions.