Ultrafast structural dynamics of in-cage isomerization of diiodomethane in solution.

ABSTRACT: Despite extensive studies on the isomer species formed by photodissociation of haloalkanes in solution, the molecular structure of the precursor of the isomer, which is often assumed to be a vibrationally hot isomer formed from the radical pair, and its in-cage isomerization mechanism remain elusive. Here, the structural dynamics of CH₂I₂ upon 267 nm photoexcitation in methanol were probed with femtosecond X-ray solution scattering at an X-ray free-electron laser. The determined molecular structure of the transiently formed species that converts to the CH₂I-I isomer has the I-I distance of 4.17 Å, which is longer than that of the isomer (3.15 Å) by more than 1.0 Å and the mean-squared displacement of 0.45 Ų, which is about 100 times larger than those of typical regular chemical bonds. These unusual structural characteristics are consistent with either a vibrationally hot form of the CH₂I-I isomer or the loosely-bound radical pair (CH₂I˙⋯I˙).

SUBMITTER: Kim H 

PROVIDER: S-EPMC8179290 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature