Figure shows a schematic of the reaction, H + + e -+ C * → CH * , where we have marked ω as it changes from the IS through the TS to the FS. Throughout this work, we define the TS as the state corresponding to the energy maximum along a reaction path (see Methods section in the SI). In the IS, the reacting proton is bound to H 2 O forming a hydronium ion. As the reaction proceeds, the O-H bond is stretched until reaching the TS, followed by a reduction in of the C-H bond length until reaching the FS. Within this picture, ω is 0 at the IS, 1 at the FS and any value in between 0 and 1 at the TS.