Ab - initio non-adiabatic couplings among three lowest singlet states of H₃⁺: construction of multisheeted diabatic potential energy surfaces

Abstract

We calculate the adiabatic potential energy surfaces and non-adiabatic interactions among the three lowest singlet states (1¹A', 2¹A' and 3¹A') of H₃⁺ in hyperspherical coordinates for a fixed hyperradius, ρ = 9 bohr as functions of hyperangles, Θ (0 < Θ < 90°) and ɸ (0 < ɸ < 360°). All ab initio calculations are performed using MRCI level of methodology implemented in quantum chemistry package, MOLPRO. The ground (1¹ A') and the first excited (2¹ A') states exhibit several conical intersections as functions of ɸ for Θ > 70°. Subsequently, we carry out adiabatic to diabatic transformation (ADT) to obtain ADT angles for constructing single-valued, continuous, smooth and symmetric 3 × 3 diabatic potential energy matrix to perform accurate scattering calculations.