X-ray induced Coulomb explosion imaging of transient excited-state structural rearrangements in CS2

Abstract

Structural imaging of transient excited-state species is a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. However, separating the electronic and nuclear contributions to the spectroscopic observables is challenging, and typically requires the application of high-level theory. Here, we employ site-selective ionisation via ultrashort soft X-ray pulses and time-resolved Coulomb explosion imaging to interrogate structural dynamics of the ultraviolet photochemistry of carbon disulfide. This prototypical system exhibits the complex motifs of polyatomic photochemistry, including strong non-adiabatic couplings, vibrational mode couplings, and intersystem crossing. Immediately following photoexcitation, we observe Coulomb explosion signatures of highly bent and stretched excited-state geometries involved in the photodissociation. Aided by a model to interpret such changes, we build a comprehensive picture of the photoinduced nuclear dynamics that follows initial bending and stretching motions, as the reaction proceeds towards photodissociation.

The Role of Momentum Partitioning in Covariance Ion Imaging Analysis

“…Classical trajectory calculations of point charges interacting under Coulomb’s law can provide a useful guide for interpreting Coulomb explosion images. ,,, A model that assumes instantaneous fragmentation and purely electrostatic repulsion is generally only a good approximation for the Coulomb explosion of highly charged polycations, which fragment promptly into exclusively ionic products . However, through modifications that build on this basic framework, more complex fragmentation processes can be modeled, such as the three-body sequential breakup. ,, Here, we extend this methodology to simulate the three-body sequential breakup of a molecular dication, which yields ionic and neutral products.…”

“…These correlations reveal substantial detail about the underlying fragmentation process, such as the nuclear dissociation dynamics and the time scales over which these dynamics evolve . Covariance imaging − is a complementary method that allows experiments to be performed at higher count rates (i.e., under conditions in which many molecules are ionized in a given experimental cycle) while still extracting physically meaningful multiparticle correlations through statistical analysis. − This method is particularly well suited to experiments at current low-repetition rate FEL sources, where conducting experiments at a higher count rate can greatly expedite data acquisition.…”

Time-Resolved X-ray Photoelectron Spectroscopy: Ultrafast Dynamics in CS2Probed at the S 2p Edge

“…The ion data will be presented in a separate manuscript. 33 A more detailed account of the experimental apparatus and the data processing steps is given in Methods and the Supporting Information .…”