Linear and nonlinear X-ray spectra of chiral molecules: X-ray Circular Dichroism, Sum- and Difference-Frequency Generation of fenchone and cysteine
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| Format: | Preprint |
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2025
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| _version_ | 1866913664759496704 |
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| author | Nam, Yeonsig Chergui, Majed Young, Linda Rouxel, Jérémy R. |
| author_facet | Nam, Yeonsig Chergui, Majed Young, Linda Rouxel, Jérémy R. |
| contents | Recent advancements in X-ray light sources at synchrotrons and X-ray free-electron lasers (XFELs) present exciting opportunities to probe molecular chirality using novel nonlinear spectroscopies with element-sensitivity. Circular dichroism (CD) and sum- and difference-frequency generation (SFG/DFG) are established techniques for probing molecular asymmetry in optical regime, with SFG/DFG offering unique advantages due to their background-free nature and independence from circularly polarized light sources. Extending them into the X-ray domain provides deeper insights into local structural asymmetries by leveraging the localized nature of core orbitals. In this work, we simulate X-ray absorption spectroscopy (XAS), X-ray circular dichroism (XCD) and nonlinear optical/X-ray SFG and DFG (OX SFG/DFG) signals for two prototypical chiral molecules, fenchone and cysteine. Our multi-reference simulations reproduce experimental data when available and reveal how novel X-ray spectroscopies exploit the site- and element-sensitivity of X-rays to uncover molecular asymmetry. The XCD spectra show strong asymmetries at chiral centers, while distant atoms contribute less. The OX SFG/DFG signals, under fixed resonant optical excitation, strongly depend on core transition and valence excitation energies. This dependence allows us to introduce two-dimensional (2D) chirality-sensitive valence-core spectroscopy, which provides insight into the overlap between valence orbitals and local molecular asymmetry. Finally, our estimates using realistic laser and X-ray pulse parameters demonstrate that such nonlinear experiments are feasible at XFELs, offering a promising tool for investigating the geometric and electronic structures of chiral molecules. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2501_14671 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Linear and nonlinear X-ray spectra of chiral molecules: X-ray Circular Dichroism, Sum- and Difference-Frequency Generation of fenchone and cysteine Nam, Yeonsig Chergui, Majed Young, Linda Rouxel, Jérémy R. Chemical Physics Recent advancements in X-ray light sources at synchrotrons and X-ray free-electron lasers (XFELs) present exciting opportunities to probe molecular chirality using novel nonlinear spectroscopies with element-sensitivity. Circular dichroism (CD) and sum- and difference-frequency generation (SFG/DFG) are established techniques for probing molecular asymmetry in optical regime, with SFG/DFG offering unique advantages due to their background-free nature and independence from circularly polarized light sources. Extending them into the X-ray domain provides deeper insights into local structural asymmetries by leveraging the localized nature of core orbitals. In this work, we simulate X-ray absorption spectroscopy (XAS), X-ray circular dichroism (XCD) and nonlinear optical/X-ray SFG and DFG (OX SFG/DFG) signals for two prototypical chiral molecules, fenchone and cysteine. Our multi-reference simulations reproduce experimental data when available and reveal how novel X-ray spectroscopies exploit the site- and element-sensitivity of X-rays to uncover molecular asymmetry. The XCD spectra show strong asymmetries at chiral centers, while distant atoms contribute less. The OX SFG/DFG signals, under fixed resonant optical excitation, strongly depend on core transition and valence excitation energies. This dependence allows us to introduce two-dimensional (2D) chirality-sensitive valence-core spectroscopy, which provides insight into the overlap between valence orbitals and local molecular asymmetry. Finally, our estimates using realistic laser and X-ray pulse parameters demonstrate that such nonlinear experiments are feasible at XFELs, offering a promising tool for investigating the geometric and electronic structures of chiral molecules. |
| title | Linear and nonlinear X-ray spectra of chiral molecules: X-ray Circular Dichroism, Sum- and Difference-Frequency Generation of fenchone and cysteine |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2501.14671 |