Abstract
We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the carbon disulphide molecule near the sulfur K-absorption edge. We observe a strong evolution of the RIXS spectral profile with the excitation energy tuned below the lowest unoccupied molecular orbital (LUMO) absorption resonance. The reason for this is twofold. Reducing the photon energy in the vicinity of the LUMO absorption resonance leads to a relative suppression of the LUMO contribution with respect to the emission signal from the higher unoccupied molecular orbitals, which results in the modulation of the total RIXS profile. At even larger negative photon-energy detuning from the resonance, the excitation-energy dependence of the RIXS profile is dominated by the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. Furthermore, our study demonstrates that in the hard x-ray regime, localization of the S 1s core hole occurs in during the RIXS process because of the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Core-hole localization leads to violation of the symmetry selection rules for the electron transitions observed in the spectra.
- Received 25 December 2014
DOI:https://doi.org/10.1103/PhysRevX.5.031021
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Published by the American Physical Society
Popular Summary
The behavior of molecules exposed to x-ray radiation is of interest to physicists, chemists, and biologists in light of the many technological and medical applications of the process. A key question is how the electrons and atoms in molecules respond to the x-ray radiation and whether one can follow this response in real time. Tracing extremely fast x-ray-induced electron dynamics in a molecule occurring on attosecond () time scales may be accomplished using very short x-ray pulses; this technique is currently in development. Here, we theoretically and experimentally study the rearrangement of the molecule in order to demonstrate alternative access to fast electron dynamics.
Resonant photoexcitation of electrons in the sulfur K shell excites the molecule to a highly unstable state that decays via the emission of x-ray radiation. The x-ray emission spectra carry information about the electronic structure and the dynamic processes occurring in the core-excited molecule. Detuning the excitation photon energy below the absorption resonance effectively reduces the delay of emission from , as determined by the lifetime of the excited state, to the low-attosecond time scale. By tracing the evolution of the emitted x-ray spectra, which persists for detunings of up to 10 eV, we show that more core-excited states are involved in the inelastic x-ray scattering when the energy detuning is increased. We predict that at large detunings, a coherent excitation of multiple electronic states launches electron dynamics on the attosecond time scale determined by the spacing between the coherently excited intermediate states.
Our work demonstrates that resonant x-ray emission spectroscopy can be effectively used in studies of electron dynamics in core-excited molecules. Our theoretical predictions, which may be tested in the foreseeable future, propose an alternative experimental approach in the rapidly developing field of attophysics.