Dynamics of Hydrogen Bond Breaking Induced by Outer-Valence Intermolecular Coulombic Decay

The photoexcitation of weakly bound complexes can lead
to several
decay pathways, depending on the nature of the potential energy surfaces.
Upon excitation of a chromophore in a weakly bound complex, ionization
of its neighbor upon energy transfer can occur due to 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 the evidence for outer-valence ICD induced by multiphoton
excitation by near-ultraviolet radiation of 4.4 eV photons, hitherto
unknown in molecular systems. In the binary complexes of 2,6-difluorophenylacetylene
with aliphatic amines, a resonant two-photon excitation localized
on the 2,6-difluorophenylacetylene chromophore results in the formation
of an amine cation following an outer-valence ICD process. The unique
trends in experimentally observed translational energy distribution
profiles of the amine cations following hydrogen bond dissociation,
analyzed with the help of electronic structure and ab initio molecular dynamics calculations, revealed the presence of a delicate
interplay of roaming dynamics, methyl-rotor dynamics, and binding
energy.