A new potential energy surface and rovibrational spectra of the CO–CO2 complex: Dependence on the antisymmetric stretching vibration of CO2.

We present a new ab initio five-dimensional potential energy surface for the CO–CO2 complex containing the Q3 normal mode for the ν3 asymmetric stretching vibration of the CO2 unit. The potential was calculated by the supermolecular approach at the explicitly correlated coupled cluster [CCSD (T)-F12a] level with aug-cc-pVTZ basis set plus midpoint bond functions. Two vibrationally averaged four-dimensional potentials for CO–CO2 with CO2 at the ground and ν3 excited states were generated by the integration of the five-dimensional potential over the Q3 intramolecular coordinate. Each potential displays a T-shaped global minimum with the C end in the CO unit pointing toward the C atom in the CO2 unit and a T-shaped local minimum but with the CO monomer rotated by 180°. The rovibrational bound states and energy levels for the CO–CO2 dimer were obtained employing the radial discrete variable representation/angular finite basis representation method in conjunction with the Lanczos algorithm. The vibrational ground and some lower excited states for CO–CO2 are localized around the global minimum because of the higher potential barriers. The band origin is blueshifted by 0.2089 cm−1 for CO–CO2 in the CO2ν3 range, which is consistent with the experimental result of 0.211 cm−1. The geared bending vibrational frequencies for CO–CO2 are 24.7101 and 24.5549 cm−1 at the ground and ν3 excited states of CO2, respectively. The predicted rovibrational frequencies, as well as spectral constants, coincide with the available observations, and these parameters show that the CO–CO2 complex is a nearly prolate asymmetric rotor. [ABSTRACT FROM AUTHOR]