Three-dimensional covariance-map imaging of molecular structure and dynamics on the ultrafast timescale

Abstract

Ultrafast laser pump-probe methods allow chemical reactions to be followed in real time, and have provided unprecedented insight into fundamental aspects of chemical reactivity. While evolution of the electronic structure of the system under study is evident from changes in the observed spectral signatures, information on rearrangement of the nuclear framework is generally obtained indirectly. Disentangling contributions to the signal arising from competing photochemical pathways can also be challenging. Here we introduce the new technique of three-dimensional covariance-map Coulomb explosion imaging, which has the potential to provide complete three-dimensional information on molecular structure and dynamics as they evolve in real time during a gas-phase chemical reaction. We present first proof-of-concept data from recent measurements on CF3I. Our approach allows the contributions from competing fragmentation pathways to be isolated and characterised unambiguously, and is a promising route to enabling the recording of ‘molecular movies’ for a wide variety of gas-phase chemical processes.

Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging

“…As such, the transformation into the recoil frame can only be made in the detector plane. This restriction can be circumvented in a three-dimensional velocity-map imaging experiment 54 . In the case of two ions recoiling at approximately 180 degrees from one another, the 'true' covariance signal is focused to a relatively small region of the covariance map, as a result of this transformation into the recoil frame.…”

Multi-mass velocity-map imaging studies of photoinduced and electron-induced chemistry

“…Such methods can be applied both to photodissociation experiments and to Coulomb explosions. We have very recently acquired the first proof-of-concept data for such an approach during a recent set of Coulomb explosion imaging experiments performed at the Artemis ultra-fast laser facility 72 . Figure 13 shows part of a preliminary 3D-sliced covariance-map imaging data set, in which the pairwise recoil of I + and CF3 + ions formed in the Coulomb explosion of CF3I 2+ is captured in three dimensions.…”

Covariance-Map Imaging: A Powerful Tool for Chemical Dynamics Studies

“…It is also possible to generate three-dimensional covariance maps from a pair of three-dimensional velocity-map images recorded using slice imaging. 3D covariances of this type have been demonstrated recently by Lee et al 20,54 for various Coulomb explosion products of multiply-charged CF 3 I ions.…”