INFLUENCE OF ELECTRON CORRELATION-EFFECTS ON CALCULATED PROPERTIES AND VIBRATIONAL-SPECTRA OF FF-NH3 AND FCL-NH3 CHARGE-TRANSFER COMPLEXES

Ab initio calculations have been performed to investigate the molecula r structure and vibrational spectra of FF ... NH3 and FCl ... NH3 char ge transfer complexes. The two dimensional potential energy surface V( r(XF), R(N ... F)), where X = F, Cl, is obtained by using 6-31G* and 6-311G* basis sets at the SCF level. The correlation effects are inve stigated at the MP2 level. The coefficients of the potential energy su rface are obtained by an analytical fit to a polynomial expansion up t o the fourth or sixth orders. The stretching vibrations deduced from V (r(XF), R(N ... F)) are calculated by means of a variational treatment including a convergence study. Ir is shown that electron correlation effects must be taken into account to provide reliable stretching vibr ations. The results are finally compared with the available experiment al data.