Collision-induced dissociation reaction dynamics of the acetone molecular ion

The collision-induced dissociation (CID) reaction CH3COCH+3 + Ar → CH3CO+ + CH3 + Ar has been studied with a tandem hybrid mass spectrometer (a high-resolution mass spectrometer coupled with a supersonic neutral beam, which uses post-collision energy and mass analysis) at ion laboratory energies in the range 4.5–300 eV. Kinetic energy and angular distributions of the fragment CH3CO+ ions were measured and scattering contour diagrams for this process were constructed. The results show that the dissociation proceeds via low-impact parameter collisions with extensive momentum transfer. At 4.5 eV, the product is primarily backward scattered with some intensity at the center-of-mass (completely inelastic collision). At higher energies the product ion is progressively more forward scattered but over the energy range investigated the maximum intensity never shifts to 0°. Collectively, these results suggest that impulsive mechanisms dominate CID reactions at all energy ranges for this ion and that the dominant mechanism is kinematically different at low and high energy.