Delayed Dissociation and Transient Isomerization during the Ultrafast Photodissociation of the Tribromomethane Cation

We present a time-resolved measurement of the photodissociation and photoisomerization dynamics of bromoform (CHBr₃) in the mono- and di-cationic states produced by near-infrared (NIR) strong-field ionization. The dissociation process is probed by NIR-induced Coulomb explosion imaging. We find that for dissociation channels involving production of HBr and Br₂ fragments, which require the formation of new bonds, the dissociation appears to be delayed with respect to the primary C-Br bond dissociation channel. Ab initio molecular dynamics simulations support the observed delay. Moreover, the simulations suggest that reaction pathways involving transient isomerization via H- and Br-migration in the CHBr₃ monocation are responsible for the formation of the HBr and Br₂ fragments.