Anharmonic vibrational frequencies and vibrationally averaged structures and nuclear magnetic resonance parameters of FH F¹

The anharmonic vibrational frequencies of FH F- 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 (1), 1292 (2), 1313 (3), 1837 (1 + 3), and 1864 cm-1 (1 + 2), the zero-point H-F bond length (r0) at 1.1539 Å, the zero-point one-bond spin-spin coupling constant [J01 (HF)] at 124 Hz, and the bond dissociation energy (D0) at 43.3 kcalmol. They agreed excellently with the corresponding experimental values: 1 =583 cm-1, 2 =1286 cm-1, 3 =1331 cm-1, 1 + 3 =1849 cm-1, 1 + 2 =1858 cm-1, r0 =1.1522 Å, J01 (HF) =124±3 Hz, and D0 =44.4±1.6 kcalmol. 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- (3) and low-frequency (1) stretching modes was examined and found to explain semiquantitatively the appearance of a 1 progression on 3. Our calculations predicted a value of 186 Hz for experimentally inaccessible J02 (FF).