Ion and neutral beams merge to measure reactions under cold interstellar medium conditions

Collisions between ions and neutral atoms are fundamental processes in many fields, from astronomy to plasma physics, as well as industrial applications. In the cold interstellar medium, this type of collision drives the formation of molecules in the gas phase.

At the Cryogenic Storage Ring (CSR) of the Max Planck Institute for Nuclear Physics, Grussie et al. employed a merged beams technique to obtain energy-resolved measurements between fast neutral atoms and ions in well-defined quantum state.

“To use the same technique for ion-neutral collisions at storage rings has not been possible in the past, owing to the difficulties in combining a fast, well-defined neutral atom beam with high intensity and the ultra-high vacuum of the storage ring,” said author Florian Grussie. “Our research demonstrates that these difficulties can be overcome.”

The team created a neutral beam using laser neutralization of a negative carbon ion beam. The neutral atoms are directed into a straight section of the CSR, where they meet and react with a beam of stored molecular ions. After guiding the products out of the ring, the group counts them with a single-particle detector.

By detuning the energy of the incoming neutral beam, the researchers can adjust the relative energy between the two species and measure the reaction probability as a function of relative collision energy.

This new capability will allow future experiments involving a whole class of molecular ions of astrophysical interest.

“Once this experiment runs routinely, there are a lot of very fundamental reactions that we can study to further our knowledge of the formation and destruction of molecules in interstellar clouds and the early universe,” said Grussie.

Source: “An ion-atom merged beams setup at the Cryogenic Storage Ring,” by F. Grussie, A. P. O’Connor, M. Grieser, D. Müll, A. Znotins, X. Urbain, and H. Kreckel, Review of Scientific Instruments (2022). The article can be accessed at https://doi.org/10.1063/5.0086391 .