Local frame transformation theory for two classes of diatomic molecules

This study develops an alternative, analytical approach for computing the electronic spectra of long-range diatomic Rydberg molecules with charged atomic cores in which either each core is identical, or else one core is a bare ion with no screening. This approach involves a frame transformation between locally separable regions of the configuration space, and an analytic expression for the frame transformation matrix is derived for ∑ states. Results for ²∑ states of LiH⁺ ₂ and LiH⁺ are compared with available theoretical calculations.