Fragmentation dynamics of CH₃Cl (q = 2,3): theory and experiment

A combined theoretical and experimental study of the dissociation of the di- and trication of the CH₃Cl molecule has been performed. Experimentally, these multi-charged ions were produced after interactions of a CH₃Cl effusive jet with a mono-energetic beam of H⁺ or Ar⁹⁺ projectile ions. Theoretically, we mapped the multi-dimensional potential energy surfaces of CH₃Cl²⁺, H₂CClH²⁺ and CH₃Cl³⁺ species in their electronic ground and electronically excited states using post-Hartree-Fock configuration interaction methods. In addition to the obvious bond-breaking ionic fragments (i.e. H⁺ + CH₂Cl⁺, H⁺ + CH₂Cl²⁺ and CH₃⁺ + Cl⁺), the formation of H₂⁺ (+CHCl⁺ or CHCl²⁺), H₃⁺ (+CCl⁺) and HCl⁺ (+CH₂⁺) was observed upon bond rearrangement after ion impact of CH₃Cl. The interaction strength of the incident projectiles is found to affect the relative yields on the observed dissociation channels, however, it has no effect on the kinetic energy releases of the fragmentation pathways. For the observed dissociation channels, plausible formation mechanisms were proposed. These reaction pathways take place on the ground and/or electronic excited potential energy surfaces of the doubly and triply charged CH₃Cl ions, where spin-orbit and vibronic couplings are in action. Moreover, this work suggests that the mechanisms undertaken may depend on the multiply charged ion preparation by valence or inner-shell single photon photoionization, fast ion beam impact or ultrafast intense laser ionization.