Pisa Composite Schemes Meet Master Equation Modeling for Accurate Pressure-Dependent Kinetics: HCI Elimination from...

Area of Science:

• Computational Chemistry
• Chemical Kinetics
• Reaction Dynamics

Background:

• Accurate prediction of temperature- and pressure-dependent kinetics is crucial for understanding complex chemical processes.
• Unimolecular reactions, such as HCl elimination, present significant challenges in kinetic modeling.
• Existing computational methods often lack the accuracy or efficiency required for detailed kinetic analyses.

Purpose of the Study:

• To develop and validate an integrated computational protocol for predicting temperature- and pressure-dependent kinetics of unimolecular reactions.
• To apply the protocol to the competing HCl elimination channels of 2-chloropropene.
• To achieve subchemical-accuracy predictions at a feasible computational cost.

Main Methods:

• Utilized the Pisa Composite Schemes (PCS) framework, combining PCS2 geometries with PCS3 energies and TQλ contributions for high accuracy.
• Employed an interoperable tool with analytical gradients for robust composite-level geometry optimizations and Intrinsic Reaction Coordinate (IRC) calculations.
• Incorporated anharmonic corrections via second-order vibrational perturbation theory and solved the 1-D master equation using the Master Equation System Solver software.

Main Results:

• Achieved subchemical-accuracy (better than 0.25 kcal mol⁻¹) for the reaction system.
• Computed activation barrier for the dominant propyne-forming channel (ΔH₀‡ = 65.54 kcal mol⁻¹) closely matches experimental shock-tube measurements (within 0.3%).
• Successfully predicted pressure-dependent rate constants and branching ratios for competing HCl elimination pathways.

Conclusions:

• The proposed computational framework provides a robust and systematically improvable strategy for predictive kinetics.
• The protocol enables quantitative support for detailed combustion modeling and shock-tube kinetic analyses.
• Offers a feasible computational cost for achieving high-accuracy kinetic predictions.