Our latest publication addresses a long-standing challenge in understanding the UV photochemistry of bromoform (CHBr₃), focusing on the elusive mechanisms driving the production of atomic and molecular bromine fragments. Using gas-phase ultrafast megaelectronvolt electron diffraction (MeV-UED) with femtosecond resolution, we directly capture the structural dynamics following 267 nm photon excitation. Our findings reveal that isomerization, specifically forming the iso-CHBr₃ (Br-CH-Br-Br) isomer, plays a substantial role alongside direct C–Br bond cleavage in the early stages of reaction. Remarkably, about 60% of the molecules undergo isomerization within the first few hundred femtoseconds. These results align well with ab initio molecular dynamics simulations and suggest a roaming mechanism, providing new insights into the competing pathways in bromoform photochemistry.

This work was led by the Gessner group (LBNL) in collaboration with the Centurion group (U Nebraska-Lincoln), our group and a number of colleagues from SLAC and UC Berkeley. First author Lars was a master student in the Zuerch Lab when we were still at the Fritz Haber Institute in Berlin and he is now jointly advised by Oliver Gessner and Michael.

The paper got published in the Journal of the American Chemical Society:
https://pubs.acs.org/doi/full/10.1021/jacs.4c07165