Calculated evolution of the population of rotational states of HeH⁺ ions during storage inside the CSR. The simulation is based on the published transition strengths and level energies of Coppola et al. (2011). The calculation is the same as presented by Novotný et al. (2019), where the initial distribution represents a thermal ensemble at 3000 K. However, the exact choice of the initial temperature is largely irrelevant, as all highly excited states decay very quickly compared to the storage times of up to 60 s that were sampled in the present experiment.