Abstract
The proton transfer reaction H3+ + CO is one of the cornerstone chemical processes in the interstellar medium. Here, the dynamics of this reaction have been investigated using crossed beam velocity map imaging. Formyl product cations are found to be predominantly scattered into the forward direction irrespective of the collision energy. In this process, a high amount of energy is transferred to internal product excitation. By fitting a sum of two distribution functions to the measured internal energy distributions, the product isomer ratio is extracted. A small HOC+ fraction is obtained at a collision energy of 1.8 eV, characterized by an upper limit of 24% with a confidence level of 84%. At lower collision energies, the data indicate purely HCO+ formation. Such low values are unexpected given the previously predicted efficient formation of both HCO+ and HOC+ isomers for thermal conditions. This is discussed in light of the direct reaction dynamics that are observed.
Highlights
The proton transfer reaction H3+ + CO is one of the cornerstone chemical processes in the interstellar medium
Formyl product cations are found to be predominantly scattered into the forward direction irrespective of the collision energy
The data indicate purely HCO+ formation. Such low values are unexpected given the previously predicted efficient formation of both HCO+ and HOC+ isomers for thermal conditions. This is discussed in light of the direct reaction dynamics that are observed
Summary
The proton transfer reaction H3+ + CO is one of the cornerstone chemical processes in the interstellar medium. Most of the product events are scattered into very low scattering angles, a fact that can be ascribed to a stripping-like process caused by high impact parameter collisions.[38] The velocity of the product ions are clearly smaller than the center-of-mass speed of the incoming neutral molecule, showing a considerably high degree of internal excitation, a fact that has been observed for related proton transfer reactions.[39,40] This hints to an efficient coupling of the reaction coordinate to the rovibrational degrees of freedom of an intermediate ion−
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