Ultrafast dissociation in polyhalogenated ethane: Alternative mechanisms

Dissociation, a simple unimolecular reaction, can be obscure, especially in complex molecules with numerous degrees of freedom. Here we suggest an ultrafast dissociation mechanism involving multimode dynamics evolving on the barrierless potential energy surface. The mechanism is elaborated from the analysis of the nuclear dynamics in X-ray excited molecules. It implies that in large molecules dissociation may yield to heavy fragments on very short timescales owing to the internal motion of light linkages. In particular, the rotation of the C2H4-moiety in 1-bromo-2-chloroethane leads to the dissociation of C-Cl or C-Br bonds in Cl2p or Br3d core-excited states in ~ 7 fs