Evidence for charge-induced dipole reaction in laser ionized van der Waals clusters: a case of Fe2+ reacting with argon atoms inside a cluster

Abstract

Fe(CO)₅-doped argon clusters have been photo-ionized by 532 nm, nanosecond laser pulses and the ions generated as a result of laser–cluster interaction were detected using time-of-flight mass spectrometry. Formation of [FeAr]⁺ was observed to coincide with generation of Fe²⁺. Reaction of singly charged iron ion (Fe⁺) with argon did not give rise to a detectable amount of [FeAr]⁺. However, for the Fe²⁺ case, the yield of [FeAr]⁺ is found to depend on the laser intensity and size of the argon cluster. Density functional theory calculations suggest that the reaction of Fe²⁺ with Ar dimer is energetically 4 times more favorable for generation of [FeAr]⁺ as compared to the reaction of Fe⁺ with Ar. Based on the intensity of different ions, two orders of magnitude enhancement in the rate constant has been estimated for the reaction of iron ion towards argon with a change of ionic state from singly charged to doubly charged. The present experimental and theoretical studies demonstrate the existence of an additional and efficient intra-cluster reaction channel based on charge-induced dipole reaction for generation of [FeAr]⁺ from the photo-ionization of Fe(CO)₅-doped argon clusters.