Adiabatic theory for high Rydberg molecules

Molecules in high Rydberg states, or high Rydberg molecules, are special types of excited species. Classically, at least one of the valence electrons of such molecules is excited to a high-energy near-threshold orbit with a negative eccentricity. Therefore, the electron spends most of its orbiting time on roaming slowly far away from the parent ionic core. With this classical picture in mind, we develop a general adiabatic theory termed the inverse Born-Oppenheimer approximation, in contrast to the conventional Born-Oppenheimer adiabatic theory for molecules in ground or lower excited states, to describe high Rydberg molecules. A thorough theoretical formulation starting from the non-relativistic molecular Hamiltonian and Schrödinger equation is presented with emphasis on the mathematical rigorousness of this theory. Quantitative calculations of the transition rate constants for many radiative and nonradiative processes involved in high Rydberg molecules are shown explicitly.