Theoretical Study of Nascent Hydration in the Fe⁺(H₂O)_<i>n</i> System

Abstract

The interactions of the iron monocation with water molecules and argon atoms in the gas phase were studied computationally to elucidate recent infrared vibrational spectroscopy on this system. These calculations employ first-principles all-electron methods performed with B3LYP/DZVP density functional theory. The ground state of Fe⁺(H₂O) is found to be a quartet (<i>M</i> = 2<i>S</i> + 1 = 4, <i>S</i> is the total spin). Different binding sites for the addition of one or two argon atoms produce several low-lying states of different geometry and multiplicity in a relatively small energy range for Fe⁺(H₂O)–Ar₂ and Fe⁺(H₂O)₂–Ar. In both species, quartet states are lowest in energy, and sextets and doublets lie at higher energies from the respective ground states. These results are consistent with the conclusion that the experimentally determined infrared photodissociation spectra (IRPD) of Fe⁺(H₂O)–Ar₂ and Fe⁺(H₂O)₂–Ar are complicated because of the presence of multiple isomeric structures. The estimated IR bands for the symmetric and asymmetric O–H stretches from different isomers provide new insight into the observed IRPD spectra