Resolved: Electronic states underneath broad absorptions

The far UV absorption spectra of many polyatomic molecules show featureless, broad bands, even though the lifetimes of the underlying electronic states can be long enough to render the states observable. Using photoionization from Rydberg states we measure electron binding energies, thereby referencing the electronic spectra to the adiabatic ionization energy. In trimethylamine, we find that the 3s, the 3 px,y, and the 3 pz Rydberg states have binding energies of 3.087, 2.251, and 2.204 eV, respectively. Vibrational motions excited while preparing the Rydberg states do not interfere with the spectra. © 2007 American Institute of Physics.