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a b s t r a c tThe isolated effect of O 2 (a 1 D g ) on the propagation of C 2 H 4 lifted flames was studied at reduced pressures (3.61 kPa and 6.73 kPa). The O 2 (a 1 D g ) was produced in a microwave discharge plasma and was isolated from O and O 3 by NO addition to the plasma afterglow in a flow residence time on the order of 1 s. The concentrations of O 2 (a 1 D g ) and O 3 were measured quantitatively through absorption by sensitive off-axis integrated-cavity-output spectroscopy and one-pass line-of-sight absorption, respectively. Under these conditions, it was found that O 2 (a 1 D g ) enhanced the propagation speed of C 2 H 4 lifted flames. Comparison with the results of enhancement by O 3 found in part I of this investigation provided an estimation of 2-3% of flame speed enhancement for 5500 ppm of O 2 (a 1 D g ) addition from the plasma. Numerical simulation results using the current kinetic model of O 2 (a 1 D g ) over-predicts the flame propagation enhancement found in the experiments. However, the inclusion of collisional quenching rate estimations of O 2 (a 1 D g ) by C 2 H 4 mitigated the over-prediction. The present isolated experimental results of the enhancement of a hydrocarbon fueled flame by O 2 (a 1 D g ), along with kinetic modeling results suggest that further studies of C n H m + O 2 (a 1 D g ) collisional and reactive quenching are required in order to correctly predict combustion enhancement by O 2 (a 1 D g ). The present experimental results will have a direct impact on the development of elementary reaction rates with O 2 (a 1 D g ) at flame conditions to establish detailed plasma-flame kinetic mechanisms.

Benzylium versus tropylium ion yields from the fragmentation of ethylbenzene cations at various excitation energies are studied by forming excited ethylbenzene cations by charge transfer from a series of chargetransfer agents and by identifying the benzylium ion by its secondary reaction with neutral ethylbenzene. At lower excitation energies, the tropylium ion yield decreases with increasing energy from values near 16% (at an energy of 230 kJ mol -1 ) to 5% (at an energy of 500 kJ mol -1 ). At higher excitation energies, the tropylium ion yield increases again, which is attributed to secondary isomerization of the vibrationally highly excited benzylium ion arising from the primary fragmentation. It is suggested that this isomerization competes with radiative cooling of the excited benzylium ion. The experimental observations are rationalized in the framework of statistical unimolecular rate theory and electronic structure calculations.

A novel ozone source was developed to study the negative ion chemistry of ozone in the gas phase. Rate constants and product ion branching fractions are reported for 17 negative ion−molecule reactions involving ozone (O3). This is the most comprehensive set of O3 reactions with negative ions to date. The reactions proceed primarily through charge transfer and O atom transfer. The reaction rate constants for O-, O2 -, and OH- are large and approximately equal to the thermal energy capture rate constant given by the Su-Chesnavich equation based on average dipole orientation theory. The negative ions NO2 -, CO4 -, SF6 -, and PO2 - are somewhat less reactive, reacting at approximately 20−50% of the thermal capture rate. The hydrofluorocarbon ions CF3 - and C2F5 - react at 80% of the thermal capture rate, and F- is the major product ion formed. NO3 -, CO3 -, PO3 -, CF3O-, F-, Cl-, and Br- are found to be unreactive with rate constants < 5 × 10-12 cm3 s-1, which is the present detection limit of our apparatus using this ozone source. The I- ion was observed to cluster with O3 to form IO3 - with a rate constant of approximately 1 × 10-11 cm3 s-1, which is a factor of 2 above our detection limit, and no other product channels were observed. All of the anions listed above showed no reactivity, k < 5 × 10-13 cm3 s-1, with O2.

The pressure and temperature dependence of the stabilization vs dissociation yield of chemically activated ethylbenzene ions from the charge-transfer reaction O 2 + + C 8 H 10 f O 2 + C 8 H 10 + is analyzed. Combining the measured data with experimental specific rate constants, k(E), for dissociation of ethylbenzene ions from the literature allows absolute values of the product Z〈∆E〉 for energy transfer in the buffer gases He and N 2 to be derived. By assigning the collision frequency Z to the Langevin rate constant, the average energies transferred per collision 〈∆E〉 for highly excited C 8 H 10 + are obtained. They are close to the corresponding values for neutral alkylbenzenes. k(E) shows a transition from values given by phase space theory at low energies to values arising from an anisotropic valence potential at higher energies. The charge transfer process is analyzed in terms of resonant charge transfer, charge transfer through ethylbenzene-O 2 + complexes, and charge transfer producing electronically excited O 2 molecules, with the former being exploited for the described study of collisional energy transfer.