Theoretical Spectroscopy of the N₂HAr⁺ Complex

The six-dimensional potential energy surface of the electronic ground state of N₂HAr⁺ is determined by ab initio computations at the CCSD(T) level of theory. The potential energy surface is used to derive a set of spectroscopic data for N₂HAr⁺ and N₂DAr⁺ using second order perturbation theory. Full six-dimensional (6-D) rotation−vibration computations are also carried out using an analytical representation of the surface for J=0 and 1, in order to deduce the rovibrational spectra of N₂HAr⁺ and its deuterated isotopomer. Our variationally determined anharmonic wavenumbers differ by less than 15 cm⁻¹ from the most accurate experimental values. Strong anharmonic resonances are found between the rovibrational levels of both cations even at low energies.