Dissociative recombination of the polyatomic ions D3O+ and H3O+ with electrons have been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Absolute cross sections have been determined from 0.001 eV to 0.25 eV center-of-mass energy for D3O+ and from 0.001 eV to 28 eV for H3O+. The cross sections are large (7.3×10−13 cm2 for D3O+ and 3.3×10−12 cm2 for H3O+ at 0.001 eV). At low energies, the cross sections for D3O+ are E−1 energy dependent whereas it is slightly steeper for H3O+. A similar E−1 energy dependence was also observed by Mul et al. [J. Phys. B 16, 3099 (1983)] with a merged electron-ion beam technique for both H3O+ and D3O+ and by Vejby-Christensen et al. [Astrophys. J. 483, 531 (1997)] with the ASTRID storage ring in Denmark, who presented relative cross sections for H3O+. A resonance has been observed around 11 eV for H3O+. It reflects an electron capture to Rydberg states converging to an excited ionic core. A similar structure was reported by Vejby-Christensen et al. Our absolute measurements are in fairly good agreement with those from Mul et al., which were first divided by 2 (Mitchell, 1999, private communication) and from Heppner et al. [Phys. Rev. A 13, 1000 (1976)] for H3O+. Thermal rates were deduced from the measured cross sections for electron temperatures ranging from 50 K to 30 000 K. At 300 K, the thermal rate is equal to 7.6×10−7 cm3 s−1 for H3O+ and to 3.5×10−7 cm3 s−1 for D3O+. Complete branching ratios for all the possible product channels have been determined from 0 eV to 0.005 eV center-of-mass energy for D3O+ and at 0 eV for H3O+, using a well-characterized transmission grid in front of an energy-sensitive surface-barrier detector. No isotope effect was observed within the experimental uncertainties. The three-body break-up channel OX+X+X (where X stands for H or D) is found to occur for 67%–70% of the dissociations. Water or heavy water is produced with an 18%–17% probability and the production of oxygen atoms is negligible. These results support the three-body break-up dominance already found by Vejby-Christensen et al. for the DR of H3O+ in a similar heavy-ion storage ring experiment. However, even if the general trend is the same for both storage rings, significant differences have been observed and will be discussed.

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The sulfur chemistry in oxyfuel combustion systems has received growing attention lately. The formation of SO 3 is of special concern, because of the elevated SO 2 concentrations found in oxyfuel, compared to air-fuel conditions. The present study focuses on the gas-phase chemistry and examines the impact of different combustion parameters and atmospheres on the formation of SO 3 in oxyfuel and air-fuel flames, using a detailed gas-phase model. The work also includes a summary of the presently available SO x data from experiments in laboratory and pilot-scale combustors. The reviewed experimental data, as well as the modeling results, show significantly increased SO 3 concentrations in oxyfuel, compared to air-fuel conditions. The modeling results reveal a complex behavior of the SO 3 formation, which is influenced by direct and indirect effects of the SO 2 , O 2 , NO x , and CO content in the flue gas. One of the main contributors to the increased SO 3 concentration in oxyfuel, compared to air-fuel conditions, is the high concentration of SO 2 in oxyfuel combustion. The modeling also shows that the stoichiometry, residence time, and flue-gas cooling rate are critical to the SO 3 formation. Thus, in addition to the stoichiometry of the flame, the flue-gas recycling conditions are likely to influence the formation of SO 3 in oxyfuel combustion.