1. Could you explain the significance of your article to the non-specialist?

The normal isotope of hydrogen is by far the dominating atom in the universe. Yet, when it comes to molecules, the fraction that is deuterated vastly exceeds what would be statistically expected. One molecule that has drawn particular attention in this respect is ammonia, believed to be formed via a series of nitrogen hydride cation intermediates. In this paper we develop a combined dynamics and statistically based model to investigate the formation of NH₂⁺, one of the ammonia precursors. Our model leads us to suggest a new explanation for how the deuterium enrichment happens during the formation of the ion. 

2. What has motivated you to conduct this work?

There are several motivations for this work. The reaction dynamics group at University of Gothenburg has a long standing interest in investigating isotope effects. In collaboration with the Copenhagen Centre for Atmospheric Research isotope effects are used to better understand the composition of Earth´s atmosphere and pin down sources and sinks for various species in the atmosphere. The choice of studying NH⁺ + H₂ and isotopes of this reaction is related to its importance in interstellar chemistry and the uncertainty that surrounds interstellar deuterium accounting. This is also one of the milestones of the European Molecular Universe network that we presently participate in. The NH₃⁺ system is also interesting simply from the fact that developing a practical yet accurate treatment is challenging.

3. Where do you see this work developing in the future?

The group in Göteborg will continue using quantum dynamics methods to study reactions of key importance in the atmosphere and interstellar space. In addition to full dynamics calculations on systems similar to that studied in this work, focus may shift to reactions occurring on and in grains to complement the gas phase work as it is has become clear that interstellar chemistry cannot be understood without understanding the chemistry occurring in and on grains.

4. Are there any particular challenges facing future research in this area?

There are huge challenges in this area. Since it is very cold in interstellar space and the densities typically are lower than the best vacuum on Earth, the understanding of interstellar chemistry relies heavily on theoretical developments. As soon as it comes to condensed phase chemistry, obtaining potential energy surfaces is a major obstacle. In addition, performing accurate dynamics studies with presently available methods becomes essentially impossible. We will have to rely on well placed approximate theories and the development of new high dimensional techniques for quantum dynamics studies. The recent development of the multilayer multiconfigurational time dependent Hartree method may be useful here.