SEARCH Articles Figures Tables Beyond the Harmonic Approximation Harmonic approximation Harmonic approximation of the potential Normal modes in the harmonic approximation The Adiabatic and Harmonic Approximations The Approximations The Ideal Gas, Rigid-Rotor Harmonic-Oscillator Approximation The Quasi-Harmonic Approximation The Rigid Rotor Harmonic Oscillator Approximation Vibrational Properties Beyond the Harmonic Approximation