LASER IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY COMBINED WITH RESIDUAL-GAS ANALYSIS FOR THE INVESTIGATION OF MODERATE TEMPERATURE BENZENEOXIDATION

The simultaneous use of 10.5-eV vacuum ultraviolet photo ionization ti me-of-flight mass spectrometry and residual gas analysis using standar d electron ionization for the study of the oxidation of a typical arom atic hydrocarbon fuel is shown to provide reliable estimates of specie s concentration, including radical reaction intermediates. The advanta ges and limitations of the combined techniques are discussed, with spe cial emphasis on the factors bringing about uncertainties in the conce ntration measurements and spurious signals arising in quantitative pho to ionization time-of-fight mass spectrometry. These factors are shown to be minimized and controllable under appropriate experimental condi tions. The results for oxidation of benzene in an argon diluent at 800 -1200 K and 30 ms mean residence time provide simultaneous semi-quanti tative measurements of the broad spectrum of both stable and labile pr oduct masses. Especially interesting features include observation of b iphenyl and C5H5 concentrations at low benzene conversions. The data a re also consistent with the previously proposed mechanism for phenoxy radical decomposition to CO and cyclopentadienyl radical. Although alt ernative pathways cannot be ruled out without further structural ident ification, especially of the C5H5 species, these data provide an oppor tunity for checks of detailed models for these reaction conditions.