Site Selective Coulomb Explosion Imaging of Excited State Structural Rearrangements in CS₂

Structural imaging of transient excited-state species remains a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. Here, we present such a study, employing site-selective ionization and time-resolved Coulomb explosion imaging to interrogate structural dynamics of ultraviolet (UV) excited carbon disulfide (CS₂). This prototypical system exhibits many of the fundamental motifs of ultrafast photochemistry, such as strong non-adiabtic coupling of several potential energy surfaces and motion along multiple nuclear coordinates. Substantial changes in the recorded three-dimensional ion momenta in the first several hundred femtoseconds following photoexcitation arise from Coulomb explosion of highly bent and stretched nuclear geometries transiently populated prior to photodissociation. Through examination of correlated ion momentum distributions and comparison to a simple classical model, a comprehensive picture of the photoinduced nuclear dynamics can be extracted, involving initial bending and stretching motion ultimately leading into photodissociation into S and CS photoproducts.