[garthfluff]

I have a UV/Visible spectra for iodine from which I have calculated the wavenumbers of all the peaks and labeled them with arbitrary numbers. If I take the area under my plot, which I understand to be D0 the dissociation energy, I get a value of around 71kJ mol-1. About half of the dissociation energy of iodine. However if I add the energy difference between the ground state and the exited state for I2, I obtain a value closer to the literature value for the dissociation of iodine, what I get is around 134kJ mol-1.

The problem is, I can not understand why I would be doing this, as I though the value of the area under the Birge-Sponer plot should give you the dissociation energy.

Do I have bad results or am I missing something completely here. It's a difficult procedure to make mistakes in, because it's not very involved experimentally.