COLLISION-INDUCED DISSOCIATION OF THE PROPANE MOLECULAR ION

A cross-beam tandem hybrid mass spectrometer equipped with a supersonic neutral beam source was used to investigate collision-induced dissociation (CID) of the propane molecular ion at a series of relative collision energies from 1.7-449 eV. The competing processes of elimination of methane and loss of methyl radical were studied using beams of helium and argon neutrals. The dynamics of both dissociation processes change relatively little with increasing collision energy, demonstrating that the CID mechanism does not change with collision energy over a very broad range. The most probable energy transfer into the ion increased only slightly with collision energy. The dynamics are consistent with previous conclusions that internal energy is randomized amongst internal degrees of freedom before dissociation. The intensity maxima at all energies occurred at non-zero scattering angles in the center-of-mass reference frame; scattering angles decrease with increasing collision energy but never decreased to zero. This implies that the CID mechanism for propane ion is dominated by small impact parameter collisions with large angular momentum exchange at all energies.