Helium-ammonia compounds predicted
Discovery that helium and ammonia can form compounds over a wide pressure range.
Helium and ammonia are both found in large quantities inside icy giant planets. Because helium is generally considered to be the most inert element in the periodic table, it is not clear whether these two components can react with each other under planetary conditions of extreme pressures and temperatures, or what kinds of states might emerge.
Using crystal structure search techniques and ab initio molecular dynamics simulations, an international team including Dr Andreas Hermann from the Centre for Science at Extreme Conditions found that helium-ammonia compounds can form over a wide pressure range.
Upon heating, these compounds are predicted to form plastic phases (with spinning molecules on periodic lattices) and superionic states (which are part liquid, part solid). The study published in Physical Review X and featured in American Physical Society review Physics, provides new and surprising insights into the properties of compounds that may exist in icy giant planets and into new chemistry and physics of helium compounds under extreme conditions.