An adiabatic energy-level expression for anharmonic hydrogen-bonded systems

An adiabatic energy-level expression is obtained for hydrogen-bonded systems X-H----Y without neglecting the anharmonicity of the proton motion, treating the anharmonicity of the X----Y motion perturbatively or omitting many of the terms that couple the fast and slow motions. The energy-level expression is applied to FH----O (CH3)2. The reliability of the adiabatic energy-level expression is tested by comparing the adiabatic energy levels with variational energy levels.