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

Abstract

New six-dimensional ab initio potential energy surfaces (PESs) for the N2–CO2 complex, which involve the stretching vibration of N2 and the Q3 normal mode for the ν3 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 oN2–CO2 and pN2–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 N2–CO2 infrared spectra with CO2 at the ν3 zone, which coincides with the experimental data of +0.483 74 cm−1. The frequencies of the in-plane geared-bending for N2–CO2 at the ν3 = 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 ν3 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.