Multireference configuration interaction calculations have been carried out on the ground electronic state of the fluoronium ion FH2 +. Both local (expansion about equilibrium geometry) and global (expansion about linear equidistant geometry) surface fits are obtained. The equilibrium geometry occurs at Re = 1.812 35 bohr and 〈HFH = 112.30 deg. The proton affinity is 116.5 kcal/mol and the inversion barrier height is 19.25 kcal/mol. The surface is suitable for the study of large-amplitude motion, and we obtain vibrational energies up to 2 eV, which is well above the barrier height. For higher vibrational levels, we note the effect of the potential energy barrier on the vibrational spacing. The minimum in vibrational spacing for the bending progression is found to be in excellent agreement with the calculated barrier height.

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Journal The Journal of Chemical Physics
Petsalakis, I.D., Theodorakopoulos, G., Wright, J.S, & Hamilton, I.P. (1990). Potential energy surface for large-amplitude motion and vibrational spacings for FH2 +. The Journal of Chemical Physics, 92(4), 2440–2449.