Neutral production of hydrogen isocyanide (HNC) and hydrogen cyanide (HCN) in Titan's upper atmosphere

Following the first detection of hydrogen isocyanide (HNC) in Titan's atmosphere, we have devised a new neutral chemical scheme for hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) in the upper atmosphere of Titan. To improve the chemistry of HNC and HCN, a careful review of the literature has been performed to retrieve critical reaction rates and to evaluate their uncertainty factors. We have also estimated the reaction rates of 48 new reactions using simple capture theory. Our photochemical model gives abundances of HNC and HCN in reasonable agreement with observations. An uncertainty propagation study shows large uncertainties for HNC. A global sensitivity analysis pinpoints some key reactions to study as a priority to improve the predictivity of the model. In particular, our knowledge of the isomerization of HNC via the reaction H + HNC ! HCN + H and the chemistry of H2CN needs to be improved [9].

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