On Routes to Ultrafast Dissociation of Polyatomic Molecules

Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core-shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C-Cl or C-Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ~7 fs.