Dunham expansion

Dunham expansion is a mathematical technique used in molecular spectrometry and quantum mechanics to describe the energy levels of diatomic molecules. It is particularly useful for approximating the vibrational and rotational energy levels of molecules that can be modeled as harmonic oscillators or rigid rotors. The Dunham expansion expresses the energy levels of a molecule in terms of a power series in the vibrational quantum number \( v \) and rotational quantum number \( J \).