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Ultrafast Dynamics Studied by Few-Femtosecond Soft X-ray Transient Absorption Spectroscopy


X-ray Transient Absorption Spectroscopy (XTAS) has enabled real time measurements of numerous physical processes of great chemical importance. The technique is sensitive to electronic and molecular structure with element specificity and short time resolution. However, XTAS experiments that can probe carbon-containing molecules are still in their infancy. An apparatus is designed and constructed that provides efficient X-ray flux to probe transitions from the carbon 1s shell to the valence levels. The apparatus is able to use a visible pump pulse, less than 5 fs in duration, and a few-femtosecond cross-correlation is established. In vibrational studies of small molecules, core-excited potential energy surfaces along the symmetric stretch normal mode are extracted. Other vibrational modes are not observed, and the reasons are discussed as a limitation of XTAS. Dissociation of strong-field ionized CCl4+ is tracked in real time, measuring a time scale associated with Jahn-Teller distortion in this system. The signal also shows two previously unobserved intermediates in a symmetry-broken covalently bonded form of CCl4 + and a non-covalently bonded complex between a CCl3+ moiety and atomic Cl. Additionally, an excited state that results in Cl+ and CCl3 is observed. Finally, experiments measuring the electronic properties of solid-state systems are undertaken that show similar recombination times in semiconducting and metallic-containing single-walled carbon nanotube bundles, among other results.

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