Theoretical prediction of HRgCO+ ion (Rg=He, Ne, Ar, Kr, and Xe)

Ab initio quantum chemical methods have been employed to investigate the structure, stability, charge redistribution, and harmonic vibrational frequencies of rare gas (Rg=He, Ne, Ar, Kr, and Xe) containing HRgCO⁺ ion. The Rg atoms are inserted in between the H and C atoms of HCO⁺ ion and the geometries are optimized for minima as well as transition state using second order Møller-Plesset perturbation theory, density functional theory, and coupled-cluster theory [CCSD(T)] methods. The HRgCO⁺ ions are found to be metastable and exhibit a linear structure at the minima position and show a nonlinear structure at the transition state. The predicted ion is unstable with respect to the two-body dissociation channel leading to the global minima (HCO⁺+Rg) on the singlet potential surface. The binding energies corresponding to this channel are -406.4, -669.3, -192.3, -115.4, and -52.2 kJ mol^-1 for HHeCO⁺, HNeCO⁺, HArCO⁺, HKrCO⁺, and HXeCO⁺ ions, respectively, at CCSD(T) method. However, with respect to other two-body dissociation channel, HRg⁺+CO, the ions are found to be stable and have positive energies except for HNeCO⁺ at the same level of theory. The computed binding energies for this channel are 15.0, 28.8, 29.5, and 29.1 kJ mol^-1 for HHeCO⁺, HArCO⁺, HKrCO⁺, and HXeCO⁺ ions, respectively. Very high positive three-body dissociation energies are found for H+Rg+CO⁺ and H⁺+Rg+CO dissociation channels. It indicates the existence of a very strong bonding between Rg and H atoms in HRgCO⁺ ions. The predicted ions dissociate into global minima, HCO⁺+Rg, via a transition state involving H-Rg-C bending mode. The barrier heights for the transition states are 22.7, 10.1, 13.1, and 15.0 kJ mol^-1 for He, Ar, Kr, and Xe containing ions, respectively. The computed two-body dissociation energies are comparable to that of the experimentally observed mixed cations such as ArHKr⁺, ArHXe⁺, and KrHXe⁺ in an electron bombardment matrix isolation technique. Thus HRgCO⁺ cations may also be possible to prepare and characterize similar to the mixed cations (^RgHRg')+ in low temperature matrix isolation technique.