Bond-forming and electron-transfer reactivity between Ar²⁺ and O₂

Area of Science:

• Physical Chemistry
• Chemical Physics
• Atomic and Molecular Collisions

Background:

• Understanding ion-molecule reactions is crucial for various fields, including plasma physics and atmospheric chemistry.
• The reactivity of doubly charged argon ions (Ar2+) with neutral molecules like oxygen (O2) presents complex reaction dynamics.
• Previous studies have explored similar systems, but detailed insights into the reaction mechanisms and intermediates are often limited.

Purpose of the Study:

• To elucidate the reactivity, energetics, and dynamics of bimolecular reactions between Ar2+ and O2.
• To identify and characterize the different product ion channels formed during these collisions.
• To investigate the role of collision complexes and reaction intermediates in the observed reaction pathways.

Main Methods:

• Employed a position-sensitive coincidence methodology to study the reactions.
• Investigated collisions at a specific energy of 4.4 eV.
• Analyzed the mass and momentum of product ions to determine reaction channels and dynamics.

Main Results:

• Observed four distinct bimolecular reaction channels: Ar+ + O2+, Ar+ + O+, ArO+ + O+, and O+ + O+.
• The Ar+ + O+ + O channel was the most intense, with evidence for a short-lived [ArO2]2+ collision complex.
• Identified direct O- abstraction as the mechanism for ArO+ formation, likely in an excited electronic state.

Conclusions:

• The reaction between Ar2+ and O2 proceeds through multiple pathways, including single electron transfer, O- abstraction, and dissociative double electron transfer.
• The formation of a transient [ArO2]2+ complex plays a significant role in the dominant Ar+ + O+ + O channel.
• The study provides detailed insights into the complex dynamics and energetics governing these ion-molecule interactions.