Physical Mechanism of the Crossover of Ground State Energy Levels in Linear H⊗h Systems

Abstract

The icosahedral H⊗h Jahn-Teller (JT) system has vibronic ground states of H and A symmetries. Previous calculations have shown that the H state is lowest in weak coupling but that as the coupling increases, a crossover occurs. Thus the A state becomes the ground state in strong coupling. Calculations reported here show that the origin of the crossover is related to the existence of two types of tunnelling paths on the lowest adiabatic potential energy surface (APES). In weak coupling, tunnelling along a C1-type path is favoured whilst in strong coupling a C2 path is favoured. The two paths have different Berry phases, which results in a change in sign of the splitting between the states as deduced using the WKB approximation.