The X˜²B₁, ²B₂, ²A₁, and ²A₂ states of oxygen difluoride cation (F₂ O⁺) : high-level ab initio calculations and simulation of the ultraviolet photoelectron spectrum of F₂O

Abstract

The ultraviolet photoelectron spectrum of F₂O was recorded with a higher resolution than previously published. New vibrational structure was observed in the second and third bands. Near state-of-the-art molecular orbital calculations were performed on the X˜¹ A₁ state of F₂O and the X˜²B₁ , ²B₂, ²A₁ , and ²A₂ state of F₂O⁺, and their potential energy functions were computed. Spectral simulations based on Franck–Condon factor calculations including the Duchinsky effect were carried out within the harmonic oscillator model and also with the inclusion of anharmonicity, in order to assist spectral assignment. Based on the computed ionization energies obtained with the coupled cluster and multireference configuration interaction methods with basis sets of up to quintuple zeta quality, the order of the low-lying cationic states of F₂O⁺ has been firmly established. However, the detailed assignment of the overlapping second and third photoelectron bands was only achieved with the aid of spectral simulation. The iterative Franck–Condon analysis (IFCA) procedure was carried out for the first band {F₂O⁺ (X˜²B₁) ← F₂O(X˜¹ A ₁ )} in the photoelectron spectrum. With the geometrical parameters of F₂O (X˜ ¹ A ₁ ) being fixed at the available experimental values, geometrical parameters of the X˜²B₁ state of F₂O⁺ were derived. Based on anharmonic Franck–Condon factor calculations, the recommended IFCA geometrical parameters for the ground state of F₂O⁺ are R(FO)=1.323±0.002Å and <FOF=107.3±0.2°.