Potential energy surface of the CO2-N2 van der Waals complex

Four-dimensional potential energy surface (4D-PES) of the atmospherically relevant CO2-N-2 van der Waals complex is generated using the explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in conjunction with the augmented correlation consistent triple zeta (aug-cc-pVTZ) basis set. This 4D-PES is mapped along the intermonomer coordinates. An analytic fit of this 4D-PES is performed. Our extensive computations confirm that the most stable form corresponds to a T-shape structure where the nitrogen molecule points towards the carbon atom of CO2. In addition, we located a second isomer and two transition states in the ground state PES of CO2-N-2. All of them lay below the CO2 + N-2 dissociation limit. This 4D-PES is flat and strongly anisotropic along the intermonomer coordinates. This results in the possibility of the occurrence of large amplitude motions within the complex, such as the inversion of N-2, as suggested in the recent spectroscopic experiments. Finally, we show that the experimentally established deviations from the C-2v structure at equilibrium for the most stable isomer are due to the zero-point out-of-plane vibration correction. (C) 2015 AIP Publishing LLC.