Theoretical Prediction of Noble Gas Inserted Thioformyl Cations: HNgCS+ (Ng = He, Ne, Ar, Kr, and Xe)

The existence of new interesting insertion compounds, HNgCS+ (Ng = He–Xe), have been predicted theoretically through insertion of a noble gas atom into the thioformyl cation, HCS+. Second-order Møller–Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD­(T)) based techniques have been used to explore the structure, energetics, charge distribution, and harmonic vibrational frequencies of these compounds. These predicted ions are found to be energetically stable with respect to all the possible 2-body and 3-body dissociation pathways, except the 2-body channel leading to the global minimum products (HCS+ + Ng). Nevertheless, all these ions are found to be kinetically stable with a finite barrier height corresponding to their transition states, which are connected to their respective global minima products. The results obtained from charge distribution as well as atoms in molecules (AIM) analysis suggest that these ions can be best described as [HNg]+CS. Strong covalent character in the H–Ng bond is supported by the high positive energy value corresponding to the 3-body dissociation pathways. Thus, it might be possible to prepare the HNgCS+ ions in a glow discharge containing H2S, CO, and noble gas under cryogenic conditions through matrix isolation technique.