An experimental and theoretical investigation into the electronically excited states of para-benzoquinone

We report on a combination of experimental and theoretical investigations into the structure of electronically excited para-benzoquinone (pBQ). Here synchrotron photoabsorption measurements are reported over the 4.0-10.8 eV range. The higher resolution obtained reveals previously unresolved pBQ spectral features. Time-dependent density functional theory calculations are used to interpret the spectrum and resolve discrepancies relating to the interpretation of the Rydberg progressions. Electron-impact energy loss experiments are also reported. These are combined with elastic electron scattering cross section calculations performed within the framework of the independent atom model-screening corrected additivity rule plus interference (IAM-SCAR + I) method to derive differential cross sections for electronic excitation of key spectral bands. A generalized oscillator strength analysis is also performed, with the obtained results demonstrating that a cohesive and reliable quantum chemical structure and cross section framework has been established. Within this context, we also discuss some issues associated with the development of a minimal orbital basis for the single configuration interaction strategy to be used for our high-level low-energy electron scattering calculations that will be carried out as a subsequent step in this joint experimental and theoretical investigation.M.M. acknowledges the Portuguese National Funding Agency FCT-MCTES through PD/BD/106038/2015 and together with PLV the research Grant No. UID/FIS/00068/ 2013. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, PD/00193/2010); UID/Multi/04378/2013 (UCIBIO). G.G. acknowledges partial financial support from the Spanish Ministerio de Economia, Industria y Competitividad (Project No. FIS2016-8440), and the EU Project No. FP7-ITN-ARGENT- 608163. The authors wish to acknowledge the beam time at the ASTRID2 synchrotron at ISA, Aarhus University, Denmark. We also acknowledge the financial support provided by the European Community’s Seventh Framework Programme (FP7/2007-2013) CALIPSO under Grant Agreement No. 312284. M.J.B. acknowledges the Australian Research Council for some financial support. M.T.N.V. and M.A.P.L. acknowledge financial support from FAPESP, while R.F.C., M.T.N.V., M.H.F.B., and M.A.P.L. acknowledge financial support from CNPqPeer Reviewe