Coclers, L., Bouche, R., Vanclef, A., Bontemps, R., & Nielsen, C. (1981). Force-constant Calculations Using the Simplex-method Application To Imidazolidinetrione (parabanic Acid). Spectroscopy Letters : an international journal for rapid communication, 14(7), 481-498. https://doi.org/10.1080/00387018108062609 (Original work published 1981)