Showing papers by "Ivan Powis published in 2022"
TL;DR: In this paper , an experimental X-ray photoelectron circular dichroism (PECD) study of liquid fenchone at the C 1s edge was performed on a liquid microjet.
Abstract: We present an experimental X-ray photoelectron circular dichroism (PECD) study of liquid fenchone at the C 1s edge. A novel setup to enable PECD measurements on a liquid microjet [Malerz et al., Rev. Sci. Instrum., 2022, 93, 015101] was used. For the C 1s line assigned to fenchone's carbonyl carbon, a non-vanishing asymmetry is found in the intensity of photoelectron spectra acquired under a fixed angle in the backward-scattering plane. This experiment paves the way towards an innovative probe of the chirality of organic/biological molecules in aqueous solution.
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TL;DR: In this article , the absolute photoabsorption cross section of imidazole and 1-methylimidazoles was measured from threshold up to 10.8 eV using synchrotron radiation.
Abstract: The absolute photoabsorption cross section of imidazole, and that of 1-methylimidazole, have been measured from threshold up to 10.8 eV using synchrotron radiation. For each molecule, the absorption spectrum exhibits several broad bands due to transitions into excited valence states and some sharp structure associated with Rydberg states. Assignments have been proposed for some of the observed absorption bands using calculated transition energies and oscillator strengths. Quantum defect analyses have also helped guide these assignments. Natural transition orbital plots indicate that many of the electronically excited states have a mixed Rydberg/valence character. This mixing leads to irregularities in both the transition energies and the relative intensities of the absorption bands ascribed to Rydberg states. The vibrational progressions belonging to some of the Rydberg states have been interpreted using simulations of the corresponding cation’s vibrational structure obtained within the Franck-Condon model employing harmonic frequencies and normal modes. GRAPHICAL ABSTRACT
TL;DR: In this paper , the photoelectron angular distributions associated with those correlation satellites that arise predominantly through conjugate shake-up mechanisms are shown to be isotropic, while the anisotropy parameters associated with satellites due to normal shakeup processes exhibit a dependence on electron kinetic energy.
Abstract: The Kr 3d correlation satellites have been studied experimentally by using plane polarized synchrotron radiation to record polarization dependent photoelectron spectra (PES), and theoretically by employing the R-matrix method to calculate photoionization cross sections, PES and angular distributions. The experimental spectra have allowed the photoelectron anisotropy parameters characterizing the angular distributions, and the intensity branching ratios, related to the photoionization partial cross sections, to be evaluated. The results are discussed in terms of normal and conjugate shake-up processes. The experimental and calculated photoelectron angular distributions associated with those correlation satellites that arise predominantly through conjugate shake-up mechanisms are shown to be isotropic. In contrast, the anisotropy parameters associated with satellites due to normal shake-up processes exhibit a dependence on electron kinetic energy similar to that of the anisotropy parameters corresponding to the Kr 3d main lines. The theoretical results include an analysis of the partial waves representing the emitted photoelectron and, for certain correlation satellites, show that a particular ionization continuum dominates. This, in turn, may allow the dominant normal or conjugate shake-up mechanism forming the satellite to be identified.
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TL;DR: In this article , the authors demonstrate that using core-level photoemission enables probing the chiral electronic structure and its relaxation dynamics with atomic site sensitivity with an enhanced C-atom site selectivity compared to that achievable in the ground state molecule.
Abstract: Chiral molecules are widespread in nature, playing a fundamental role in bio-chemical processes and in the origin of life itself. The observation of dynamics in chiral molecules is crucial for the understanding and control of the chiral activity of photo-excited states. One of the most promising techniques for the study of photo-excited chiral systems is time-resolved photoelectron circular dichroism (TR-PECD), which offers an intense and sensitive probe for vibronic and geometric molecular structure as well as electronic structures, and their evolution on a femtosecond timescale. However, the non-local character of the PECD effect, which is imprinted during the electron scattering off the molecule, makes the interpretation of TR-PECD experiments challenging. In this respect, core-photoionization is known to allow site- and chemical-sensitivity to photelectron spectroscopy. Here we demonstrate that TR-PECD utilising core-level photoemission enables probing the chiral electronic structure and its relaxation dynamics with atomic site sensitivity. Following UV pumped excitation to a 3s Rydberg state, fenchone enantiomers (C 10 H 16 O) were probed on a femtosecond scale using circularly polarized soft X-ray light pulses provided by the free-electron laser FERMI. C 1s binding energy shifts caused by the redistribution of valence electron density in this 3s-valence-Rydberg excitation allowed us to measure transient PECD chiral responses with an enhanced C-atom site-selectivity compared to that achievable in the ground state molecule. These results represent the first chemical-specific and site-specific, enantio-sensitive observations on the electronic structure of a photo-excited chiral molecule and pave the way towards chiral femtochemistry probed by core-level photoemission.