WATER-NETWORK MEDIATED, ELECTRON INDUCED PROTON TRANSFER IN ANIONIC [C5H5N·(H2O)n]− CLUSTERS: SIZE DEPENDENT FORMATION OF THE PYRIDINIUM RADICAL FOR n ≥ 3

Abstract

As an isolated species, the radical anion of pyridine (Py$^{-}$) exists as an unstable transient negative ion, while in aqueous environments it is known to undergo rapid protonation to form the neutral pyridinium radical [PyH$^{(0)}$] along with hydroxide. Furthermore, the negative adiabatic electron affinity (AEA) of Py$^{-}$ can become diminished by the solvation energy associated with cluster formation. In this work, we focus on the hydrates [Py$cdot$(H$_{2}$O)$_{n}$]$^{-}$ with n = 3-5 and elucidate the structures of these water clusters using a combination of vibrational predissociation and photoelectron spectroscopies. We show that H-trasfer to form PyH$^{(0)}$ occurs in these clusters by the infrared signature of the nascent hydroxide ion and by the sharp bending vibrations of aromatic ring CH bending