Reactions between resonance-stabilized radicals: propargyl + allyl.

Area of Science:

• Chemical kinetics
• Theoretical chemistry
• Reaction dynamics

Background:

• The reaction between allyl and propargyl radicals is crucial for understanding complex chemical processes.
• Previous studies suggested significant formation of cyclic species, but detailed kinetic analysis was lacking.

Purpose of the Study:

• To perform a detailed theoretical analysis of the allyl and propargyl reaction system.
• To characterize the potential energy surface and calculate rate coefficients using advanced theoretical methods.
• To determine the pressure and temperature dependence of various product channels.

Main Methods:

• High-level electronic structure calculations were used to map the potential energy surface.
• Conventional transition-state theory (TST) and variational TST were applied to calculate rate coefficients.
• A time-dependent, multiple-well master equation was employed to simulate the reaction kinetics.
• Microcanonical and J-resolved rate coefficients were computed.

Main Results:

• The formation of cyclic c-C(6)H(7) and c-C(6)H(8) species is significantly suppressed at elevated pressures.
• Variational TST was crucial for accurately describing barrierless association/dissociation processes.
• Phenomenological rate coefficients, k(T,p), were determined for multiple product channels.
• The previously assumed importance of five-membered ring formation was re-evaluated.

Conclusions:

• The formation of cyclic products in the allyl-propargyl reaction is less dominant than previously thought, especially under higher pressures.
• The theoretical framework provides a robust understanding of the reaction kinetics and product distribution.
• This study offers a simplified kinetic model and accurate rate coefficients for the system.