Speaker
Description
The photodissociation of alkyl iodides has long served as a benchmark for understanding nonadiabatic molecular dynamics following ultraviolet excitation1. Allyl iodide provides an interesting extension to this family owing to the resonance stabilization of the allyl radical, which is expected to modify the excited-state potential energy landscape and influence the dissociation mechanism.
Here, we investigate the femtosecond photodissociation dynamics of allyl iodide at 200 nm using pump–probe velocity map imaging. Time-resolved detection of the iodine photofragments is achieved through state-selective Resonance Enhanced Multiphoton Ionization (REMPI) of both I and I*. Complementary measurements were carried out employing an intense 800 nm probe induce Coulomb explosion, providing complementary information on the structural evolution of the molecule during fragmentation. The combination of state-selective fragment detection and Coulomb explosion imaging provides a comprehensive picture of the competing ultrafast pathways following photoexcitation.
In contrast to the typical picosecond predissociation characterizing the dynamics induced at 200 nm in saturated alkyl iodides2, a fast dissociation occurring within 200 fs is observed. Complementary ab initio calculations indicate that the dissociation proceeds predominantly through the ion-pair state, providing a mechanistic explanation for the remarkably short dissociation timescale. These results demonstrate how resonance stabilization dramatically reshapes the excited-state dynamics of allyl iodide and reveal a distinct photodissociation pathway compared with other alkyl iodides.