The squares of the normalized eigenvector coefficients for atoms provide the much wanted information as they disclose the effect of switching atoms between the modes, as the reaction proceeds. In the lowest energy mode (1) the mobile atom H4 has been found dominating in the vicinity of the TS point (Fig. and) as expected. Its role in the structure of this mode in the initial and final stages of the process is different. Near the RS state, the H6 atom is a dominant of this mode; its role vanishes entirely near TS (Fig. ). The H5 atom participation in (1) mode, initially nearly as high as the one of H4, falls down to zero at TS, then rises sharply, to meet the level of H4 at the end of the process, with equal share in this mode (ca. 40%). The heavy atoms appear to rest merely as spectators to this atomic mode.