Dimeric sigma* radical anions are ubiquitous, and their formation, spectroscopy and outcome can often be elucidated by density functional theory. But for shorter interfragment distances, three-electron two-center systems can be reluctant to a single-determinant description, such as the hexanitrogen radical anion. For N-6(center dot-) we show that multireference configuration interactions calculations are required to recover its characteristic electronic excitation energy, while TDDFT fails even with modern exchange-correlation functionals. The effects of vibronic couplings on the absorption spectrum are delineated based on a full quantum mechanical dynamical treatment; this study opens the door towards an accurate description of the subtle solvatochromism of hemi-bonded systems. (C) 2013 Elsevier B.V. All rights reserved.