Thermochemistry and Kinetics of the Reaction of 1-Methylallyl Radicals with Molecular Oxygen

Abstract

The kinetics of the reaction CH3CHCHCH2 + O2 ⇄ CH3CHCHCH2O2 has been studied using laser photolysis/photoionization mass spectrometry. Room-temperature decay constants of the CH3CHCHCH2 radical were determined in time-resolved experiments as a function of bath gas density ([He] = (3−24) × 1016 molecule cm-3. The rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature range 345−390 K. Equilibrium constants were determined as a function of temperature and used to obtain the enthalpy of reaction 1. At high temperatures (600−700 K), no reaction of CH3CHCHCH2 with molecular oxygen could be observed and upper limits to the rate constants were determined (1 × 10-16 cm3 molecule-1 s-1 at 600 K and 2 × 10-16 cm3 molecule-1 s-1 at 700 K). Structures, vibrational frequencies, and energies of several conformations of CH3CHCHCH2, CH3CHCHCH2O2, and CH3CH(OO)CHCH2 were calculated using ab initio ...