Kinetics and product study of the self-reactions of allyl and allyl peroxy radicals at 296 K

Abstract

The laser flash photolysis technique, coupled with UV absorption spectroscopy, has been used to investigate the UV spectra and kinetics of reactions of the allyl radical (CH2CHCH2) and the allyl peroxy radical (CH2CHCH2O2) at 296 K and total pressures near atmospheric. CH2CHCH2 radicals were generated by the 193 nm photolysis of hexa-1,5-diene–N2 mixtures, or the 248 nm photolysis of allyl iodide–N2 mixtures. The 193 nm photolysis of hexa-1,5-diene–O2–N2 mixtures was used to generate CH2CHCH2O2. The low resolution spectrum of CH2CHCH2 was characterised in the range 210–232.5 nm. The absolute absorption cross-section near the maximum, σ(220 nm)=(5.8 ± 0.8)× 10–17 cm2 molecule–1, calibrated relative to the loss of allyl iodide, is in good agreement with the single published determination. The observed time dependence of CH2CHCH2 in the various chemical systems allowed measurement of rate coefficients for the following reactions 2CH2CHCH2(+M)→ CH2CHCH2CH2CHCH2(+M)(10), CH2CHCH2+ l (+M)→ CH2CHCH2l (+M)(12), CH2CHCH2+ O2(+M)→ CH2CHCH2O2(+M)(7) The parameters obtained were k10=(3.0 ± 0.5)× 10–11, k12=(1.6 ± 0.6)× 10–10, and k7=(6 ± 2)× 10–13 cm3 molecule–1 s–1.