On the photoelectron spectrum of p-benzoquinone

A high-resolution photoelectron spectrum of p-benzoquinone in the low energy (9.5-11.5 eV) region is reported and analyzed with the aid of simulations based on high-level ab initio calculations. The results generally support the notion that the two prominent spectral features in this region are each due to a pair of final ion states. The lower energy feature beginning near 10 eV is due to oxygen lone-pair ionizations, while that beginning near 11 eV comes from pi electron removal. Contrary to previous interpretations of the spectrum, however, the results of this study indicate that the two pi states are nearly degenerate, with the strongest peak in the photoelectron spectrum representing a convolution of the corresponding pair of 0-0 ionizations. (C) 2001 American Institute of Physics.