Chemical activation of oxygen molecule by quantum electronic state selected vanadium cation: observation of spin–orbit state effects

Abstract

By employing two-colour laser pulsed field ionisation-photoion (PFI-PI) double-quadrupole-double-octopole ion-molecule apparatus, we have examined the absolute integral cross-section (σ) for the reaction between vanadium cation (V⁺) and oxygen molecule (O₂), covering the centre-of-mass kinetic energy (E_cm) range of 0.2–10.0 eV. Here, V⁺ ion was prepared exclusively in its lowest 13 spin–orbit or J-states, a⁵D_J=0-4, a⁵F_J=1-5 , and a³F_J=2-4. The formation of VO⁺ + O is identified as the only product channel for these exothermic reactions. At E_cm = 0.2–5.0 eV, the σ values for the three electronic states are found to be in the order: σ(a³F_J) > σ(a⁵D_J) > σ(a⁵F_J), whereas these cross-sections become nearly identical at E_cm = 5.0–10.0 eV. This observation has been rationalised by collision-mediated non-adiabatic electronic transitions. The J-state effect for the V⁺(a³F_{2, 3)} + O₂ reactions are unambiguously identified for the first time for a reaction involving a transition metal cation. This J-state dependent chemical reactivity observed calls for rigorous theoretical interpretation. The fact that chemical reactivity for the a⁵F_J excited state is lower than that for the a⁵D_J ground state indicates that the difference in chemical reactivity is originated from quantum-electronic-state instead of energy effects.

GRAPHICAL ABSTRACT

Keywords:

• Quantum state-selected vanadium cation
• spin-orbit state effect on chemical reactivity

Acknowledgements

This material is based upon work supported by the National Science Foundation under CHE-1763319. CYN is also grateful to Dr Huie Tarng Liou for his generous donation of research support for the Ng Laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Yih Chung Chang http://orcid.org/0000-0002-3763-1864

Yuntao Xu http://orcid.org/0000-0002-1205-8168

Bo Xiong http://orcid.org/0000-0002-8985-6897

Cheuk-Yiu Ng http://orcid.org/0000-0003-4425-5307

Additional information

Funding

This material is based upon work supported by the National Science Foundation [grant number CHE-1763319].