Experimental Estlmate of the Electron-Tunnellng Distance for Some Outer-Sphere Electrochemical Reactions

The isotope effects appear as the deviation and unsymmetrization of the potential profile along the IRC in the mass-weighted Cartesian coordinate system, whereas in the ordinary nonmass-weighted Cartesian coordinate system they appear as the differences of the effective mass. The analysis of tunneling probability has shown that the difference in the effective mass which is greatest in the vicinity of the transition state extends to the considerably extended region along the IRC. In such a case where a light species transfers as a proton exchange, the tunneling process is significant. Several authorslb** have noted that the tunneling paths "cut the corner" rather than pass through the saddle point. Reduction of the multidimensional motion of the consitituting atoms to the one-dimensional motion along the reaction coordinates, s, has enabled us to analyze the complicated nature of chemically reacting systems, in particular attending the isotope effects. In the future, the tracing of the reaction pathway using the concept of the IRC will be profitable in applications to more complicated biochemical systems.