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arXiv · 1408.4696

Reaction Studies of Neutral Atomic ${\rm C}$ with ${\rm H_3^+}$ using a Merged-Beams Apparatus

A. P. O'Connor·X. Urbain·J. Stützel·K. A. Miller·N. de Ruette·M. Garrido·D. W. Savin
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Abstract

We have investigated the chemistry of ${\rm C + H_3^+}$ forming CH$^+$, CH$_2^+$, and CH$_3^+$. These reactions are believed to be some of the key gas-phase astrochemical processes initiating the formation of organic molecules in molecular clouds. For this work we have constructed a novel merged fast-beams apparatus which overlaps a beam of molecular ions onto a beam of ground-term neutral atoms. Here we present cross section data for forming CH$^+$ and CH$_2^+$ at collision energies from $\approx 9$ meV to $\approx20$ and 3 eV, respectively. Using these data we have derived thermal rate coefficients for reaction temperatures from $\approx72$ K to $\approx2.3 \times 10^5$ and $3.4 \times 10^4$ K, respectively. For the formation of CH$_3^+$ we are able only to put an upper limit on the rate coefficient. Our results for CH$^+$ and CH$_2^+$ are in good agreement with the mass-scaled results from a previous ion trap study of ${\rm C + D_3^+}$ at a reaction temperature of $\sim 1000$ K. At molecular cloud temperatures our thermal rate coefficient for forming CH$^+$ lies a factor of $\sim 2-4$ below the Langevin rate coefficient currently given in astrochemical databases and below the published semi-classical calculations. Our results for CH$_2^+$ formation are a factor of $\sim 26$ above the semi-classical results. Astrochemical databases do not currently include this channel.

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A. P. O'Connor, X. Urbain, J. Stützel, K. A. Miller, N. de Ruette, M. Garrido, D. W. Savin. 2015-04-27. Reaction Studies of Neutral Atomic ${\rm C}$ with ${\rm H_3^+}$ using a Merged-Beams Apparatus. https://doi.org/10.1088/0067-0049%2F219%2F1%2F6

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