HeH⁺ line flux ratio predicted by RADEX for the two detected ro-vibrational lines (υ, J) = (1,1) → (0,2) [P(2)] and (1,0) → (0,1) [P(1)] as a function of the rate coefficient ratio for the excitation transitions (0,0) → (1,1) and (0,0) → (1,0). The hatched blue area represents the observed ratio. The red and green circles denote the predicted line ratio when using the CB (default) or MQDT rate coefficients for the excitation (0,0) → (1,1). See text for more details.