Experimental Evidence for Double Intermolecular Coulombic Decay in Bio-Relevant Molecular Dimers.

We report the experimental observation of double intermolecular Coulombic decay (dICD) and reveal its potential for radiation biology in some prototypical molecular dimers consisting of benzene, pyridine, and water. In dICD, the inner-shell vacancy is filled by an electron from an outer shell and the energy released is transferred to doubly ionize the neighboring molecule with the emission of two low-energy electrons. The system further relaxes by a three-body Coulomb explosion process, e.g., CH_{3}^{+}+C_{5}H_{3}^{+}+C_{6}H_{6}^{+} for benzene dimer. Through multicoincidence momentum imaging, we find that dICD is an efficient relaxation pathway for the Auger-accessible inner-shell ionization states in molecular complexes. Moreover, this ultrafast decay mechanism causes a direct breaking of the aromatic rings, which is observed to be a general phenomenon occurring in biological systems and thus can play an important role in radiation biology.