Total charge-exchange cross section versus velocity of incident impactor: (a) α particles in reaction (8) He²⁺ + H₂O and (b) protons in reaction (14) H⁺ + H₂O. For He²⁺ impact on H₂O, the data at 400 km s^-1 (blue dot) of Greenwood et al. (2004) is used. For a proton impact at 400 km s^-1, the interpolated experimental value of (Lindsay et al. 1997; red dot) lies between the “ORNL” recommendation of Barnett et al. (1990) and the theoretical curve of Mada et al. (2007). The experimental values of Berkner et al. (1970) and Cable (1970) are displayed for comparison with uncertainties.