A DFT Study on the Direct CF₂ Fragmentation Mechanisms of 1,3-C₄F₆ and 1,3-C₄F₆⁺ in Plasma

Elucidation of the CF₂ generation mechanism in 1,3-C₄F₆ gas plasma has been one of the important issues for experimental and theoretical researchers because of the importance of the CF₂ radical in plasma etching processes. To determine the direct CF₂ fragmentation mechanisms of 1,3-C₄F₆ in the S₀, T₁, and cationic D₀ states, the reaction geometry, electron transfer, and molecular orbital transformation were investigated by applying the DFT(ɷB97X-D/aVTZ) method. The direct CF₂ (S₀) formation by C–C double bond rupture of 1,3-C₄F₆ (S₀) proceeds while maintaining the trans-bent structure by dative bonding interaction between CF₂ and its counterpart. 1,3-C₄F₆ (T₁) preferentially produces the CFCFCF₂ (T₁) and CF₂ (S₀) fragments following a linear reaction course. This process can be explained using a stepwise electron-sharing interaction model. 1,3-C₄F₆⁺ (D₀) generates a CF₂ (S₀) radical rather than CF₂ (T₁) and CF₂⁺ (D₀). The CF₂ fragmentation process in D₀ is also described using the electron-sharing interaction model but proceeds along the trans-rocking pathway, featuring electron oscillations between the CFCFCF₂ and CF₂ moieties in the C–C distance range of 1.8–2.6 Å. These findings provide insight into CF₂ generation of CF₂-containing perfluoro-olefins as potential alternatives to c-C₄F₈ and valuable information to establish the high-reliable 1,3-C₄F₆ plasma chemistry database essential to plasma simulations.