Dissociation of fluoromethane trication induced by highly charged ion collisions

Investigating molecular fragmentation mechanisms and the kinetic energy distributions of fragments provides crucial insights into their roles in plasma physics, radiation-induced damage in biological tissues, and interstellar chemistry. In this study, we conducted collision experiments between 3 keV/u Ar⁸⁺ ions and CH₃F molecules using a cold target recoil ion momentum spectrometer. We focused on the three-body fragmentation channel H⁺ + CH²⁺ + F⁺ resulting from C-F and C-H bond cleavage in CH₃F³⁺ ions, and measured the three-dimensional momentum vectors of all fragment ions. The fragmentation mechanism involved was analyzed using ion-ion kinetic energy correlation spectra, Newton diagrams, Dalitz plots and other correlation spectra. Our results reveal two distinct dissociation mechanisms for the H⁺ + CH²⁺ + F⁺ channel, i.e., concerted and sequential fragmentation, with the former one being dominant. In the sequential fragmentation process, H⁺ and the intermediate CH₂F²⁺ are firstly formed, followed by further fragmentation of the intermediates into CH²⁺ and F⁺. No sequential pathways involving HF²⁺ or CH₃²⁺ intermediates were identified. Furthermore, we observed two types of concerted fragmentation processes with different dynamical characteristics, suggesting that hydrogen atoms in CH₃F³⁺ may occupy different chemical environments. This phenomenon could originate from either molecular isomerization producing different structural geometries or the Jahn-Teller effect leading to inequivalent C-H bonds. This study reveals the three-body dissociation dynamics of CH₃F³⁺ induced by highly charged ion collisions, highlighting the significant role of the Jahn-Teller effect or molecular isomerization in the ionic dissociation of polyatomic molecules.