A while back I asked about How good is the Morse potential at describing the potential energy of a chemical bond as a function of stretching of the bond length?
Today I learnt (from Atkins Physical Chemistry text) that Birge-Sponer extrapolation plots provide a means to test the potential all the way up to the disassociation limit. One plots the difference in energy/frequency between neighbouring transitions. If the plot is linear and then where it extrapolates provides a means to determine the disassociation energy.
There is a nice article in Journal of Chemical Education which describes how all of this is (or can be) done in undergraduate Physical Chemistry labs. Pity I missed out...