Ab initio investigation of force fields structure and oscillation spectra of complex fluorine-containing ions LiAFsub(k)sup(+) (A-Li,Be,B)

Potential surfaces (ps) of Li2F+, LiBeF2+ and LiBF3+ are clculated by the lcao method in the two-exponent basis of grouped Gaussian functions: (9s4p/4s2p)-Li, (9s5p/4s2p)-Be, b, f. Separate ps points have been clarified with the basis comprising d-functions on fluorine atoms. It has been found that Li2F+ and LiBeF2 have a linear equilibrium Dsub(infinity h) and Csub(infinity v) symmetry configuration, respectively, while LiBF3+ - plane monodentate configuration of a Csub(2v) symmetry. A cyclic Csub(2v)-structure of LiBeF2+ and Csub(2v)-bidentate one of LiBFhl3+ are saddle points on PSs of the ions. Csub(3v) - tridentate structure of LiBF3+ is not bound. Force field coefficients, normal oscillation frequencies, ir spectra intensities and thermodynamic functions of Li2f+ and LiBeF2+ ions are calculated. Malliken populations analysis is performed. The results obtained are compared with the data of a previous ab ini itio investigation of the series of LiH+, LiBeH2+ and LiBH3+ ion-hydrides