  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.
