The spin changes on the electron-donor side (RsvH3) and electron-acceptor side (HO2 • ) were well correlated with the changes in the π-electrons of RsvH3. The spins also demonstrate that the TS is electronically characterized by delocalization of the π-electrons over the HB complex of the components. As a result, the IRC revealed that an intra-complex PCET between RsvH3 (at 4'OH) and HO2 • occurs in a concerted one-kinetic process without generating intermediates, that is a kinetically superior process agreeing with the electrochemical result.