Non-adiabatic coupling in the potential energy surfaces of SO 2 molecule.

To investigate the potential energy surfaces and the coupling between the adiabatic states of SO 2 molecules, it is necessary to consider the non-adiabatic coupling terms (NACTs), where the Born-Oppenheimer approximation breaks down. In this work, we analyze the conical intersections between 1 1 A 1 and 1 1 B 2 states (the A' states in C s symmetry) and 1 1 A 2 and 1 1 B 1 states (the A'' states in C s symmetry) using NACTs and adiabatic-to-diabatic transformation (ADT) angles. Our results confirm reasonable interaction between 1 1 A 1 and 1 1 B 2 states and strong interaction between 1 1 A 2 and 1 1 B 1 states.