Anharmonic vibrational frequencies and vibrationally averaged structures and nuclear magnetic resonance parameters of FHF-.

The anharmonic vibrational frequencies of FHF- were computed by the vibrational self-consistent-field, configuration-interaction, and second-order perturbation methods with a multiresolution composite potential energy surface generated by the electronic coupled-cluster method with various basis sets. Anharmonic vibrational averaging was performed for the bond length and nuclear magnetic resonance indirect spin-spin coupling constants, where the latter computed by the equation-of-motion coupled-cluster method. The calculations placed the vibrational frequencies at 580 (ν1), 1292 (ν2), 1313 (ν3), 1837 (ν1+ν3), and 1864 cm-1 (ν1+ν2), the zero-point H–F bond length (r0) at 1.1539 Å, the zero-point one-bond spin-spin coupling constant [1J0(HF)] at 124 Hz, and the bond dissociation energy (D0) at 43.3 kcal/mol. They agreed excellently with the corresponding experimental values: ν1=583 cm-1, ν2=1286 cm-1, ν3=1331 cm-1, ν1+ν3=1849 cm-1, ν1+ν2=1858 cm-1, r0=1.1522 Å, 1J0(HF)=124±3 Hz, and D0=44.4±1.6 kcal/mol. The vibrationally averaged bond lengths matched closely the experimental values of five excited vibrational states, furnishing a highly dependable basis for correct band assignments. An adiabatic separation of high- (ν3) and low-frequency (ν1) stretching modes was examined and found to explain semiquantitatively the appearance of a ν1 progression on ν3. Our calculations predicted a value of 186 Hz for experimentally inaccessible 2J0(FF). [ABSTRACT FROM AUTHOR]