A New Ab Initio Potential Energy Surface and Rovibrational Spectra for the CO-N₂O Complex

We constructed a new ab initio potential energy surface (PES) for CO-N₂O which includes the intramolecular Q₃ normal coordinate for the N₂O ν₃ antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular Q₃ coordinate, we obtained the vibrationally averaged PESs for the CO-N₂O system in the ground and ν₃ excited states of N₂O. Each PES features one nearly T-shaped global minimum and one skewed T-shaped local minimum. Based on these obtained PESs of CO-N₂O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν₃ vibrational band origin shift of the N₂O monomer in CO-N₂O is 2.7570 cm^-1, matching well with the observed value of 2.9048 cm^-1. The computed microwave and infrared transition frequencies, as well as the rotational parameters, are consistent with the experimental observations.