Comparison of the Fleshman et al. (2012) cross-section fits to the H₂O⁺ + H₂O collision cross section measurements by Lishawa et al. (1990) for reactions (R1; red line) and (R2; blue line) with the cross-section values used by Mendis et al. (1986; shaded gray area) as a function of the relative energy of the reacting pair. The ion energy range sampled by RPC-IES is given by the tan box (may be shifted toward lower energy for a negative S/C potential).