A method used to calculate the heat of dissociation of a molecule by extrapolation from observed band spectra. The dissociation energy D₀ is equal to the sum of the vibrational quanta Δ‎G, where Δ‎G represents the energy between two successive vibrational states. This means that D₀ is approximately equal to the area under the curve of Δ‎G plotted against the vibrational quantum number v. If the first few vibrational quanta are observed, an approximate value of D₀ can be obtained by a linear extrapolation of this curve. If a sufficient number of vibrational quanta have been observed, a considerable improvement in the value of D₀ can be obtained by taking the curvature of the Δ‎G curve into account by quadratic (and/or) higher terms. The technique was put forward by Raymond Birge (1887–1980) and Hertha Sponer (1895–1968) in 1926.