Storage ring measurements of the dissociative recombination of H ₃⁺

The dissociative recombination (DR) of H₃⁺ is a key process in interstellar chemistry. More than 30 experimental studies of the DR process have been published in the literature. The H₃⁺ DR rate coefficient results obtained from these measurements, however, have not always been consistent. The outcome seems to depend on the experimental method, on the exact measurement procedure and sometimes even on the interpretation of the experimental data. In the past two decades, heavy-ion storage rings have become the working horse for DR measurements, as they provide a direct measurement of the DR products. Furthermore, storage ring measurements yield energy-resolved rate coefficients with unprecedented resolution that allow for detailed comparison with theory. DR results from different storage ring facilities have shown a remarkable consistency throughout the years and they provide additional information on break-up dynamics and internal excitation. In this study, we will review the storage ring DR measurements that have been carried out for H₃⁺.