The pyrolysis of 2-phenethyl phenyl ether (PPE, C_6H_5C_2H_4OC_6H_5) in a hyperthermal nozzle (300-1350 °C)
was studied to determine the importance of concerted and homolytic unimolecular decomposition pathways.
Short residence times (<100 μs) and low concentrations in this reactor allowed the direct detection of the
initial reaction products from thermolysis. Reactants, radicals, and most products were detected with
photoionization (10.5 eV) time-of-flight mass spectrometry (PIMS). Detection of phenoxy radical, cyclopentadienyl
radical, benzyl radical, and benzene suggest the formation of product by the homolytic scission of
the C_6H_5C_2H_4-OC_6H_5 and C_6H_5CH_2-CH_2OC_6H_5 bonds. The detection of phenol and styrene suggests
decomposition by a concerted reaction mechanism. Phenyl ethyl ether (PEE, C_6H_5OC_2H_5) pyrolysis was also
studied using PIMS and using cryogenic matrix-isolated infrared spectroscopy (matrix-IR). The results for
PEE also indicate the presence of both homolytic bond breaking and concerted decomposition reactions.
Quantum mechanical calculations using CBS-QB3 were conducted, and the results were used with transition
state theory (TST) to estimate the rate constants for the different reaction pathways. The results are consistent
with the experimental measurements and suggest that the concerted retro-ene and Maccoll reactions are
dominant at low temperatures (below 1000 °C), whereas the contribution of the C_6H_5C_2H_4-OC_6H_5 homolytic
bond scission reaction increases at higher temperatures (above 1000 °C)
