Conical intersections between X²A₁ and A²B₂ electronic states of NO₂

Abstract

We explore both the general symmetry-allowed accidental (SAA) conical intersections (CIs) and Renner-Teller (RT) interactions prevailed between the ground (X²A₁) and first excited (A²B₂) electronic states of NO₂ in the configuration space of normal mode coordinates. Global ab initio potential-energy surfaces and Non Adiabatic Coupling Term (NACT) between those states are reported. For each of the three pairs of normal mode (Q₁,Q₂,Q₃), calculated NACT show singularity at different positions, which are used to calculate Adiabatic-to-Diabatic Transformation (ADT) angles and thereby, the diagonal elements of ADT matrix display (i) sign change for odd number of SAA CI (s) and (ii) no sign change for even number of SAA CIs as well as Renner–Teller interactions. Similar to Jahn-Teller CI, the existence of SAA CIs are, further, confirmed by Longuet-Higgins’ phase change.