A new six-dimensional ab initio potential energy surface and rovibrational spectra for the N₂-CO₂ complex

New six-dimensional ab initio potential energy surfaces (PESs) for the N-2-CO2 complex, which involve the stretching vibration of N-2 and the Q(3) normal mode for the nu(3) asymmetric stretching vibration of CO2, were constructed using the CCSD(T)-F12/AVTZ method with midpoint bond functions. Two vibrational averaged 4D interaction potentials were obtained by integrating over the two intramolecular coordinates. It was found that both PESs possess two equivalent T-shaped global minima as well as two in-plane and one out-of-plane saddle points. Based on these PESs, rovibrational bound states and energy levels were calculated applying the radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm. The splitting of the energy levels between oN(2)-CO2 and pN(2)-CO2 for the intermolecular vibrational ground state is determined to be only 0.000 09 cm(-1) due to the higher barriers. The obtained band origin shift is about +0.471 74 cm(-1) in the N-2-CO2 infrared spectra with CO2 at the nu(3) zone, which coincides with the experimental data of +0.483 74 cm(-1). The frequencies of the in-plane geared-bending for N-2-CO2 at the nu(3) = 0 and 1 states of CO2 turn out to be 21.6152 and 21.4522 cm(-1), the latter reproduces the available experimental 21.3793 cm(-1) value with CO2 at the nu(3) zone. The spectral parameters fitted from the rovibrational energy levels show that this dimer is a near prolate asymmetric rotor. The computed microwave transitions as well as the infrared fundamental and combination bands for the complex agree well with the observed data.