Experimental Astrophysics: Quantum state determination and manipulation in mutual neutralisation experiments

Abstract

Reactions and interactions between ions in plasmas are crucial phenomena that drive the evolution of matter in the universe. Specifically, mutual neutralisation (MN) is a charge transfer collision between two oppositely charged ions, which is very efficient at the low collision energies and low temperature found in the interstellar medium. The presence of HeH+ in the early universe is thought to have significant importance in the formation of stars and was recently found in planetary nebulae, opening up new questions regarding its role. However, its presence is hard to detect by observation, and only by studying HeH+ in collisions such as MN in a laboratory, can we gain fundamental knowledge to improve our models. Here we present a final-state-resolved MN experiment of HeH+ with D− performed at the world-unique facility Double ElectroStatic Ion Ring ExpEriment (DESIREE) in Stockholm, Sweden. The MN of HeH+ and D− resulted in the three neutral products He(1s2) + H(n = 2) + D(1s) corresponding to a kinetic energy release of about 1 eV. A first analysis suggests that MN leading to He(1s2) + H(n = 1) + D(1s) through radiative dissociation from the intermediate HeH∗(C 2Σ+) state was also observed. We suspect this experiment to be studied again at various energies in the future, to obtain cross sections and branching ratios which can be used in models. A proof of principle MN experiment with Na+ and Si− was also conducted, namely the manipulation of the quantum state population in the ion beam by laser photodetachment. The effect of the selective depletion was visible though not complete, needing further investigation. This technique will allow for more detailed MN studies to be investigated at DESIREE in the future.