No abstract

Electronic and vibrational excitation of acrylonitrile induced by 3-50 eV energy electrons has been investigated by the electron energy loss spectroscopy. Electronic excitation spectra have been recorded for 30 and 50 eV impact energies at a 10°scattering angle in the energy loss range from 5.5 to 11.5 eV, corresponding to the excitation of electrons belonging to the outermost-valence-shell molecular orbitals. We have reviewed the assignment of the valence excited states occurring in the 5.5-9 eV energy loss region. The vibrational patterns associated with the two lowest-energy singlet valence excited states have also been re-examined. Moreover, we have proceeded for the first time to the analysis and attribution of several Rydberg series converging to the ionic ground state and to its two lowest-energy electronic excited states. The study of the excitation function of the C-H stretching modes of acrylonitrile in the 3-11 eV electron impact energy range has shown evidence of a broad shape resonance built on the electronic ground state of the molecule and centered at 5.85 eV. This resonance contributes to a preferential excitation of the C-H stretching modes suggesting that the charge distribution of the additional electron is very likely that of a *͑C-H͒ valence molecular orbital. A comparison has been made between the resonances observed in C 2 H 4 and CH 2 CHCN, in order to discuss the symmetry of the resonant state and also to analyze the substitution effect of the cyanogen group.

Detailed experimental investigation of a non-equilibrium nanosecond pulsed discharge in premixed CH 4 /air mixtures at atmospheric pressure has been carried out. The experiments demonstrated significant reductions in ignition delay and increased lean burn capability relative to conventional spark ignition. Advanced laser diagnostics have been used to identify the physical processes which lead to these improvements. The electron temperature and density properties were measured using laser Thomson scattering (LTS). Temperature measurements were performed using N 2 CARS thermometry to quantify the energy transfer in the gas mixture. Effect of the discharge on the local temperature shows the existence of the ignition of the gas mixture for equivalence ratio between 0.7 and 1.3. Fast development of a flame kernel is then observed. The experiment also shows that the flame can be sustained above the discharge due the repetitive ignition of the flame at the plasma repetition rate. Finally, OH and CH PLIF experiments were performed to confirm the large OH and CH streamer-induced production over the discharge volume.

Experimental investigation of nanosecond pulsed discharge in premixed CH4/air mixtures at atmospheric pressure has been carried out using laser diagnostics. Electron temperature and number density are measured using laser Thomson scattering. Temperature of neutral molecules is measured by CARS. Finally, OH, CH and CH2O are probed using PLIF to identify their role in the reduction of ignition delay and in the improvement of lean burn capability relative to conventional spark ignition. Measurements are compared with numerical simulations performed using CHEMKIN-based code.