Identification of isomeric C5H3 and C5H5 free radicals in flame with tunable synchrotron photoionization

Isomers of the C5H3 and C5H5 free radicals formed in benzene/oxygen flame are identified by analyzing the observed photoionization efficiency spectra with the aid of theoretical simulations based on calculated ionization energies (IEs) and Franck-Condon factors. For C5H3, the results reveal that two linear isomers (i-C5H3 and n-C5H3) are formed in the benzene flame, while, for C5H5, both linear and cyclic isomers (l-C5H5 and c-C5H5) are formed. Adiabatic IEs for i-C5H3, n-C5H3, l-C5H5 and c-C5H5 are measured to be 8.21, 8.32, 7.83 and 8.44 eV, respectively (all with an uncertainty of ±0.05 eV).