Generation of full dimensional potential energy surfaces for atmospherically important charge transfer tetratomic complexes: the case of the OMgOO+ radical cation

Abstract

The weakly bound charge transfer OMgOO⁺(²Π) ion is a quasi-linear–bent Renner–Teller system with a non-zero spin–orbit contribution. The six-dimensional potential energy surfaces (6D-PESs) for the two Renner–Teller components have been generated in internal coordinates. After benchmarking calculations, we show that the newly implemented explicitly correlated coupled cluster approach (RCCSD(T)-F12) in connection with the cc-pVTZ-F12 basis set provides an accurate description of the full 6D-PESs of this molecular system. Both components are bent with low barriers to linearity along the in-plane angles. The potentials are also very flat along the out-of-plane torsional mode. Hence, this confers a pronounced quasi linear character to OMgOO⁺. Moreover, the parts of the potentials relative to the middle bond are shallow and strongly coupled to the bending motions. The parts of the PESs corresponding to the OO and MgO external diatom stretch coordinates differ strongly from those relative to the four other internal coordinates. Special care was taken to correctly account for such behaviors during the generation of the grid and fitting procedures. The present theoretical methodology can be used for mapping the 6D-PESs of other atmospherically important charge transfer complexes presenting similar features such as ONNO⁺, O₄⁺, OOCO⁺ or M–CO₂⁺ (where M is an alkali, magnesium or aluminum metal).