Theoretical study of weakly bound dimers between hydrogen fluoride and some polar molecules

Weakly bound linear and bent dimers, FH---X (where X = CO, OC, CNH, NCH, N2O and ON2) are investigated using the DFT B3LYP and ab initio MP2 methods with the same basis sets (6-311 ++G(3df,2pd)). The strengths of the H---CorH---N H-bonds in dimers FH---CO, FH---CNH, and FH---N2O are compared with those of the H---OorH---N H-bonds in dimers FH---OC, FH---NCH, and FH---ON2. The results obtained for the H-bond distances, the elongation effect of the HF bond, the red shift of the HF stretching frequency, and the energy difference between the dimer and the charge transfer reveal that the H-bonds of the first group of dimers are stronger than those of the second. The Gibbs energies calculated for the six dimer formations indicate that the weakly bound dimers are unstable at room temperature (T = 298 K) (FH---X's -> FH + X's, Delta G < 0).