On Ambient-light-induced intermolecular Coulombic decay in unbound pyridine monomers

A recent report by Barik et al. [Nature Chemistry 14, 1098, 2022] on ambient-light-induced intermolecular Coulombic decay (ICD) in unbound pyridine monomers proposes the formation of a pyridine cation via intermolecular Coulombic decay following a three-body association/collision, wherein all the three pyridine molecules are in the excited state. The collision-free conditions of the free-jet expansion, an abysmally low probability of finding three independently excited pyridine molecules in the vicinity of each other, and extremely low excited state lifetimes negate the possibility of ICD in unbound pyridine monomers. An alternate mechanism, wherein the pyridine monomer cation originates from the dissociative ionization of pyridine dimers following a three-photon absorption process, based on the translational energy measurements of pyridine cation is proposed.