Isomer-dependent charge transfer dynamics in the dissociation of alkyl iodide isomers

Alkyl iodides have played a key role in understanding excited-state photodynamics that give rise to bond cleavage. We utilized femtosecond extreme ultraviolet (XUV) free electron laser (FEL) pulses to probe dissociation mechanisms in the alkyl iodide isomers 1-iodobutane and tert-butyl iodide (C₄H₉I). We used a 267 nm UV pump to excite the molecules and probed with a 100 eV XUV pulse that ionized the iodine 4d orbital. This ionization subsequently caused a Coulomb explosion due to Auger-Meitner decay, and the momentum of the resulting ions was measured using a velocity map imaging (VMI) spectrometer. Our study shows that energy disposal within these alkyl iodides is highly distributed towards internal degrees of freedom in molecules with linear carbon chains as opposed to those that are branched. Both isomers were found to undergo a Coulomb explosion and produce high momentum iodine ions due to charge transfer occurring between the multiply charged iodine and the alkyl cofragment, with the population of this charge transfer channel being greater in tert-butyl iodide. Additionally, our results also reveal that Coulomb explosions of the alkyl iodides caused by FEL pulses leads to different distributions of C_xH_y fragments being present for 1-iodobutane and tert-butyl iodide. Covariance mapping is used to gain more insight into the mechanisms causing this isomer-dependent charge transfer and fragmentation. Our results demonstrate that XUV-induced charge transfer depends strongly on molecular structure and provides insight into the interpretation of Coulomb explosion data.