Influence of electron correlation effects on calculated properties and vibrational spectra of FF ⋯ NH3 and FCl ⋯ NH3 charge transfer complexes

Abstract Ab initio calculations have been performed to investigate the molecular structure and vibrational spectra of FF ⋯ NH 3 and FCl ⋯ NH 3 charge transfer complexes. The two dimensional potential energy surface V(r XF , R N t F ) , where X = F, Cl, is obtained by using 6–31G ∗∗ and 6–311G ∗∗ basis sets at the SCF level. The correlation effects are investigated at the MP2 level. The coefficients of the potential energy surface are obtained by an analytical fit to a polynomial expansion up to the fourth or sixth orders. The stretching vibrations deduced from V(r XF , R N t F ) are calculated by means of a variational treatment including a convergence study. It is shown that electron correlation effects must be taken into account to provide reliable stretching vibrations. The results are finally compared with the available experimental data.