A study of electron-ion dissociative recombination of substituted benzene analogs relevant to the Titan atmosphere

Abstract

Because of the continuing success of the Cassini Mission to study the Titan atmosphere, a great deal of kinetic data is required. One of the types of kinetic data which is needed is for electron-Ion Dissociative Recombination (e-IDR) rate constants. This is used by Titan atmospheric modelers to explain, in part, the process by which simple compounds, such as nitrogen and methane, are transformed into larger compounds. The larger compounds, possibly poly-cyclic aromatic hydrocarbons (PAH’s), are responsible for the characteristic orange haze present within the Titan atmosphere. With the confirmed presence of benzene, both in the Titan atmosphere by Cassini and on the Titan surface by the Huygens probe, the e-IDR rate constant data for benzene and various benzene analogs are needed by Titan atmospheric modelers. To satisfy this need, a study of the e-IDR rate constants for benzene substituted with varying functional groups has been completed. Another study of the e-IDR rate constants for benzene with hetero-atom substitutions has also been undertaken to address the possible presence of PAH’s. When possible, the temperature dependence data have been collected for the benzene analog under study. Trends between e-IDR rate constants and the number of hetero-atom additions and between e-IDR rate constants and the Hammett σpara value are some of the observed trends in the various studies. These revealed trends in e-IDR rate constants will greatly reduced the number of e-IDR rate constants needed by Titan atmospheric modelers. The effects of isomeric form on e-IDR rate constants have also been investigated in these studies. The data on each study and its effect on Titan atmospheric modeling are discussed.