Photoelectron spectroscopy of benzoquinonide and dehydrobenzoquinone anions

The 364 nm photoelectron spectra of the dehydrobenzoquinone (1(.-)) and benzoquinonide (2(-)) anions are reported. For 1(.-), the unambiguous assignment of the origin peak yields an electron affinity (EA) of 1.859 +/- 0.005 eV. Several vibrational modes of 1 are also reported. Another minor feature at higher electron binding energy is also observed in the spectrum of 1(.-). This band does not contain any resolvable peaks and only the vertical detachment energy could be obtained. This is the first time dehydrobenzoquinone, the benzyne analogue of p-benzoquinone, is observed and characterized. The photoelectron spectrum of 2- shows no resolvable structure. The origin peak could not be assigned unequivocally because of the small Franck-Condon factor for the 0-0 transition, but an upper value of 2.18 eV for the EA of 2 was obtained. Ab initio calculations are used to help in the interpretation of the spectra and the results are utilized to simulate them.