Simple semiclassical adiabatic calculation of anharmonic cross constants of a vibrational spectral fit

A simple classical adiabatic procedure, implemented with an EBK semiclassical quantization, permits the calculation of first order cross anharmonic constants of a vibrational spectral fit and shows their dependence on the anharmonicity of the coupling and not on the intrinsic anharmonicity of the modes. These first order corrections are identical to those obtained with a quantum mechanical approach.