The radiolysis of water is ubiquitous in nature and plays a critical role in numerous biochemical and technological applications. Although the elementary reaction pathways for the ionized water have been studied, the short-lived intermediate complex and structural dynamic response after the proton transfer reaction remain poorly understood. Using liquid-phase ultrafast electron diffraction technique to measure the intermolecular O··O and O··H bonds, we captured the short-lived radical-cation complex OH(H₃O⁺) that was formed within 140 femtoseconds through a direct oxygen-oxygen bond contraction and proton transfer, followed by the radical-cation pair dissociation and the subsequent structural relaxation of water within 250 femtoseconds. These measurements provide direct evidence of capturing this metastable radical-cation complex before separation, thereby improving our fundamental understanding of elementary reaction dynamics in ionized liquid water.

The data is collected from the diffraction signal (electron counts) on 2D detector on CCD camera. Each image is saved and repeated the experimental condition many times (as a function of delay time). The raw data are 2D images and were inidividually azimuthally integrated to 1D array. Experiments is a repetition of 23 times at each delay time point and averaged to a mean value and error bar at each delay time. All the data uploaded are reduced to csv file.

For the 2D map and pair distribution, any features below ~1 Angstrom is an artifact and should be ignored.