Merged-beams rate coefficient for the reaction HeH⁺ + D → HD⁺ + He as a function of the relative collision energy, E_r. The experimental values for storage times from 5 to 60 s (black markers) have been normalized to the Langevin rate coefficient (dashed line). The error bars display statistical uncertainties on a 90% confidence level. Our new theoretical TIQM calculations for HeH⁺ ions in j = 0 and j = 1 are shown by the light blue and green lines, respectively. Our QCT calculations are shown by the solid dark blue (j = 0) and green (j = 1) lines with markers. The uncertainties for the QCT values were derived from the statistics of the trajectory calculations.