Transient hydroperoxyalkyl intermediates (•QOOH) in isopentane oxidation. II. Isomer-resolved unimolecular dynamics

Area of Science:

• Chemical kinetics
• Combustion chemistry
• Theoretical chemistry

Background:

• Understanding transient intermediates is crucial for combustion modeling.
• Hydroperoxyalkyl radicals (•QOOH) play a key role in auto-oxidation pathways.
• Isopentane oxidation involves complex radical reaction mechanisms.

Purpose of the Study:

• To characterize the unimolecular dissociation dynamics of two key •QOOH isomers in isopentane oxidation.
• To compare experimental time- and energy-resolved rates with theoretical predictions.
• To validate theoretical models for predicting radical intermediate behavior.

Main Methods:

• Time- and energy-resolved detection of hydroxyl (OH) products.
• High-level theoretical calculations for stationary-point energies and transition states.
• Application of Rice–Ramsperger–Kassel–Marcus (RRKM) theory with tunneling corrections.
• Benchmark-corrected energy calculations based on smaller alkane oxidation.

Main Results:

• Two distinct •QOOH isomers (β-Me and β-Et) were investigated.
• Experimental unimolecular dissociation rates were obtained and compared with RRKM calculations.
• Good agreement between experimental and theoretical rates validates the statistical model.
• The β-QOOH_Et isomer exhibits faster decay due to a lower energy barrier.

Conclusions:

• Both β-QOOH isomers primarily decay to hydroxyl (OH) and cyclic ether products.
• The study validates the use of RRKM theory and high-level calculations for predicting •QOOH dynamics.
• Theoretical insights into reaction barriers and decay pathways are confirmed experimentally.