CALCULATED SPECTROSCOPIC PROPERTIES FOR NEGATIVE MOLECULAR IONS AND CLUSTER IONS

Large-scale ab initio calculations, mainly at the CEPA-$1^{1}$ and $CCSD(T)P^{2}$ levels, were carried out for a number of negative molecular ions like $NO_{2}^{-}, NCO^{-},\\\\ HCC^{-}, CH_{2}N^{-}, BH_{3}^{-}, CCl_{3}^{-}, HCCO^{-}, CH_{2}CN^{-}$ and $CH_{2}NC^{-}, HCC^{-}$ exhibits a shallow energy minimum in the T-shaped configuration. High-lying rovibrational states with energies in the vicinity of the barrier to isomerization are discussed in detail. The vibrational structure of the first bands of the photoelectron spectra of $CH_{2}N^{-}, BH_{3}^{-}$ and $CCl_{3}^{-}$ has been calculated with the Franck-Condon approximation. Comparison with experiment will be made for the first two species. HCCO is calculated to have a non-linear equilibrium structure with a small barrier to linearity of $272 cm^{-1}$ (CCSD(T)/151 cGTOs). The potential energy hypersurface for the isomerization process $CH_{2}NC^{-} \\rightarrow CH_{2}CN^{-}$ is discussed. In addition, the cluster anions $F^{-}, \\ldots CH_{3}F, C1^{-}, CH_{3}F$ and $Cl^{-} CH_{3}Cl$ were studied. Their formation is accompanied by a substantial increase in the intensities of the C-Hal vibrations. E.g., the $CCl (\\nu_{3})$ vibration in $Cl^{-} \\ldots CH_{3}Cl$ is red-shifted by $93 cm^{-1}$ and gains in intensity by a factor of 6 compared to free $CH_{3}Cl$.