Birge-Sponer method

In molecular spectroscopy, the Birge–Sponer method or Birge–Sponer plot is a way to calculate the dissociation energy of a molecule. By observing transitions between as many vibrational energy levels as possible, for example through electronic or infrared spectroscopy, the difference between the energy levels, ${\displaystyle \Delta G_{v+{\frac {1}{2}}}=G(v+1)-G(v)}$ can be calculated. This sum will have a maximum at ${\displaystyle v_{max}}$, representing the point of bond dissociation; summing over all the differences up to this point gives the total energy required to dissociate the molecule, i.e. to promote it from the ground state to an unbound state. This can be written:

${\displaystyle D_{0}=\sum _{v=0}^{v_{max}}\Delta G_{v+{\frac {1}{2}}}}$

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