Protonation of molecular oxygen probed in a cold 22-pole ion trap

Details Protonation of molecular oxygen probed in a cold 22-pole ion trap Protonation of molecular oxygen probed in a cold 22-pole ion trap

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.217k&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

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Scientific paper

Barrierless bimolecular ion-molecule reactions are the drivers of interstellar chemistry, responsible for the formation of many of the >150 known molecules in space. The H_3^+ molecular ion, detected with high abundance in both diffuse and dense interstellar clouds, plays a central role in this ion-molecule chemical network. Produced by cosmic ray ionization, its main destruction process in dense molecular clouds is by proton transfer reactions to other molecular species, leading e.g., to the observed high abundance of HCO^+ in these environments via the fast, exothermic proton transfer reaction H_3^+ +CO → HCO^+ + H_2. The nearly thermoneutral reaction
H_3^+ +O_2rightleftharpoons HO_2^+ + H_2 (ho2)
was discussed by Widicus Weaver et al. as a possible sink for molecular oxygen in dense molecular clouds. Previous laboratory measurements on this proton transfer reaction, in particular under conditions representative of the interstellar medium, are very limited . Here we present the experimental determination of the forward rate coefficient and the equilibrium constant of reaction (ref{ho2}) over the astrophysical important temperature range 70-180K. The reaction was studied in a temperature variable 22-pole ion trap apparatus, the method has been described in detail previously. We are currently constructing a new ion trap apparatus, which - among other improvements - will accomodate a molecular beam source for supplying the neutral reactant. This new instrument allows the extension of kinetic studies on reaction (ref{ho2}) to even lower temperatures, circumventing the freeze-out of O_2 on the surface of the ion trap. Furthermore, we are investigating if the nearly isoenergetic proton transfer reaction can also be used to perform laser induced reaction (LIR) spectroscopy on HO_2^+. No experimental data on the vibrational or rotational spectrum of HO_2^+ exists to date, but is mandatory for its detection in the interstellar medium.

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