Interstellar chemistry of atomic nitrogen: low temperature kinetics of the N + OH and N + NO reactions.

Details Interstellar chemistry of atomic nitrogen: low temperature kinetics of the N + OH and N + NO reactions. Interstellar chemistry of atomic nitrogen: low temperature kinetics of the N + OH and N + NO reactions.

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p..92b&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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In dense interstellar clouds, where temperatures fall as low as 10 K, N-bearing species are found to stay in the gas-phase. Consequently, these molecules are used to define the prevailing physical conditions. N-bearing oxygenated species, such as nitric oxide NO are used to indirectly trace the depletion of O-bearing species such as OH and H_2O, which are not observable in these regions. Thus reactions (1) and (2) play an important role in the destruction of NO and the formation of molecular nitrogen from atomic nitrogen. They also thought to play a role in the Martian and Venusian atmospheres. However, the extrapolations of reactive rate coefficients measured at high temperatures to low temperatures are often unreliable since many exothermic neutral-neutral reactions exhibit non-Arrhenius behaviour at such low temperatures. (1) N + NO → N_2 + O and (2) N + OH → NO + H. We will present measurements using the CRESU technique over the range 50 - 300 K, coupling microwave discharge methods for the production of atomic nitrogen to resonance fluorescence or pulsed laser photolysis / laser induced fluorescence techniques. We have found that reaction (1) exhibits a small negative temperature dependence in the range 50 - 300 K which diverges from the expressions used in the astrochemical databases UMIST-06 and OSU-08. The only experimental investigation of reaction (2) to date at low temperature 103 - 294 K was performed by Smith et al.: the rate coefficients are seen to increase as the temperature decreases. The most recent theoretical study by Jorfi et al. [6] predicted lower rate coefficients and a maximum value at 80 K. New experimental results will be presented to elucidate the behavior of this reaction at low temperatures. In combination with the lastest published calculations, new recommendations for the temperature dependence of the two reaction rates will be given and the effect on astrochemical models of different media will be presented.

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