Hydrogen scrambling and high propensity for multiple neutral emissions from 1,3-butadiene dication

The two-body dissociation of the dications formed after double ionization of the smallest conjugated diene, the 1,3-butadiene, C4H6, is studied using the coincidence time-of-flight technique and quantum chemistry calculations. The dication was formed by ion-impact ionization using energetic Xe3+ projectiles. Our results show that butadiene dication has a high propensity of neutral particle emission (H/H2/C2H2) prior to two-body dissociation into two singly charged fragments. The asymmetric two-body breakup, after the emission of neutral fragments from parent butadiene dication, is observed to be twice as probable as the asymmetric two-body breakup of intact butadiene dication. Our experimental results suggest that multiple structures may be formed for several different precursor dications formed after loss of neutral particles, which is indicative of the strong role of hydrogen scrambling. The internal energy dependence and time evolution of the interplay between neutral particle emission, hydrogen scrambling, and hydrogen migration are explored using ab initio molecular dynamics simulations to support the experimental observations.