Outer Valence Intermolecular Coulombic Decay in Hydrogen-Bonded Complexes Induced by Resonant Two-Photon Excitation by 4.4 eV Photons

Abstract: Photoexcitation of van der Waals complexes can lead to several decay pathways depending on the nature of the potential energy surfaces. Upon excitation of a chromophore in a complex, ionization of its weakly bound neighbour via energy transfer happens via a unique relaxation process known as intermolecular Coulombic decay (ICD); a phenomenon of renewed focus owing to its relevance in biological systems. Herein, we report an experimental evidence of outer-valence ICD induced by multiphoton excitation by near UV radiation of 4.4 eV photons, hitherto unknown in molecular systems. In the binary complexes of 2,6-difluorophenylacetylene with aliphatic amines such as dimethylamine and trimethylamine a resonant two-photon excitation is localized on the 2,6-difluorophenylacetylene chromophore. The absorbed energy is then transferred to its hydrogen-bonded partner amine and resulting in the formation of an amine cation. The kinetic energy distribution of the amine cations is invariant with respect to the initial geometry of the binary complex. The present experimental results combined with electronic structure calculations provide valuable insights into the nature of ICD in van der Waals complexes and more importantly, the role of ICD as a fast, efficient, and prominent decay channel following excitation at modest (4.4 eV) photon energies.