Direct and Indirect Hydrogen Abstraction in Cl + Alkene Reactions

Reactions between Cl atoms and propene
can lead to HCl formation
either by direct H abstraction or through a chloropropyl addition
complex. Barring stabilizing collisions, the chloropropyl radical
will either decompose to reactants or form HCl and allyl products.
Using velocity-map imaging to measure the quantum state and velocity
of the HCl products provides a view into the reaction dynamics, which
show signs of both direct and indirect reaction mechanisms. Simulated
trajectories of the reaction highlight the role of the direct H-abstraction
pathways, and the resultant simulated scattering images show reasonable
agreement with measurement. The simulations also show the importance
of large excursions of the Cl atom far from equilibrium geometries
within the chloropropyl complex, and these large-amplitude motions
are the ultimate drivers toward HCl + allyl fragmentation. Gas-phase
measurements of larger alkenes, 2-methylpropene and 2,3-dimethylbut-2-ene,
show slightly different product distributions but still feature similar
reaction dynamics. The current suite of experiments offers ready extensions
to liquid-phase bimolecular reactions.