Stable compounds of the lightest noble gases: A computational investigation of RNBeNg (Ng = He, Ne, Ar)

The structure and stability of as yet unreported compounds with the general formula RNBeNg (Ng = He, Ne, Ar) have been theoretically investigated at various ab initio and B3LYP density functional (DFT) levels of theory. Exemplary species include the parent HNBeNg and saturated and unsatured compounds such as HONBeNg, FNBeNg, X-CH2-NBeNg, X-C(O)-NBeNg (X = H, OH, F), and C6H5-NBeNg. The thermochemical stability of these molecules, invariably characterized as true energy minima on the singlet potential energy surface, depends on two factors, namely, the energy of dissociation DeltaE into singlet RNBe and Ng and the energy difference between the singlet and triplet states of RNBe. The values of DeltaE are essentially independent of the nature of the substituent R and are around 6.5 kcal mol(-1) for Ng = He, 8.5 kcal mol(-1) for Ng = Ne, and 11.0 kcal mol(-1) for Ng = Ar. In addition, for most of the investigated RNBeNg compounds, we have found that the singlet state of RNBe is more stable than the triplet state or for RNBe, with a triplet ground state, that the singlet-triplet gap is lower than the DeltaE value given above. Therefore, our calculations support the prediction that this class of thermochemically stable RNBeNg compounds could actually be very large.