Wikipedia - Potenziale di Morse Morse potential

https://doi.org/10.1351/goldbook.MT07073
The empirical function relating the potential energy of a molecule to the inter-atomic distance r accounting for the anharmonicity of bond stretching: $E\left(r\right) = D_{\text{e}}\ (1- \text{e}^{-a\ (r- r_{\text{e}})})^{2}$ where $$D_{\text{e}}$$ is the @B00699@, $$r_{\text{e}}$$ is the equilibrium @BT07003@, and $$a$$ is a parameter characteristic of a given molecule.
See:
harmonic approximation
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1953 [Terms] [Paper]