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X-ray induced dimerization of cinnamic acid: Time-resolved inelastic X-ray scattering study.

Inkinen J, Niskanen J, Talka T, Sahle CJ, Müller H, Khriachtchev L, Hashemi J, Akbari A, Hakala M, Huotari S - Sci Rep (2015)

Bottom Line: We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects.The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light.Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Helsinki, Finland.

ABSTRACT
A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale. We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects. From the time-resolved spectra, we extracted component spectra and time-dependent weights corresponding to CA and TA. The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light. We also utilized the ability of NRIXS for direct tomography with chemical-bond contrast to image the spatial progress of the reactions in the sample crystal. Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering.

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Related in: MedlinePlus

The spectra of CA and TA from the simulations.(a) Comparison of the spectra from the simulations (solid lines, the average over all carbon atoms) to the spectra from experiment (dashed lines, the components extracted from the time-resolved spectra of the CA sample). (b–d) The individual spectral contributions from each carbon atom of CA and TA from simulations. The numbering refers to the atom labels in Fig. 1.
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f3: The spectra of CA and TA from the simulations.(a) Comparison of the spectra from the simulations (solid lines, the average over all carbon atoms) to the spectra from experiment (dashed lines, the components extracted from the time-resolved spectra of the CA sample). (b–d) The individual spectral contributions from each carbon atom of CA and TA from simulations. The numbering refers to the atom labels in Fig. 1.

Mentions: To better understand the spectral changes caused by the dimerization, we performed simulations for the spectra of CA and TA. The results of these simulations in the energy range 283–291 eV are shown in Fig. 3 panel (a) with a comparison to the measured CA and TA component spectra (see the next section for component extraction). The simulations reproduce accurately the experimentally observed shift of the maximum of peak A to higher energy in the course of the dimerization, but not the intensity decrease. For this reason, the interpretations outlined below remain somewhat tentative. The mismatch in the intensity behaviour might occur, because in the simulation, only the dipole excitations are accounted for, whereas in the experiment, also nondipole excitations are present due to significantly nonzero momentum transfer. The normalizations of the spectra are not comparable, as the simulations do not perform accurately with higher-energy excitations, which is also the reason for showing the spectra only up to 291 eV. Slight differences between the experiment and the simulation are also expected because the simulation is performed with optimized geometries of isolated molecules, whereas in the experiment, the samples are in the crystalline form.


X-ray induced dimerization of cinnamic acid: Time-resolved inelastic X-ray scattering study.

Inkinen J, Niskanen J, Talka T, Sahle CJ, Müller H, Khriachtchev L, Hashemi J, Akbari A, Hakala M, Huotari S - Sci Rep (2015)

The spectra of CA and TA from the simulations.(a) Comparison of the spectra from the simulations (solid lines, the average over all carbon atoms) to the spectra from experiment (dashed lines, the components extracted from the time-resolved spectra of the CA sample). (b–d) The individual spectral contributions from each carbon atom of CA and TA from simulations. The numbering refers to the atom labels in Fig. 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4644965&req=5

f3: The spectra of CA and TA from the simulations.(a) Comparison of the spectra from the simulations (solid lines, the average over all carbon atoms) to the spectra from experiment (dashed lines, the components extracted from the time-resolved spectra of the CA sample). (b–d) The individual spectral contributions from each carbon atom of CA and TA from simulations. The numbering refers to the atom labels in Fig. 1.
Mentions: To better understand the spectral changes caused by the dimerization, we performed simulations for the spectra of CA and TA. The results of these simulations in the energy range 283–291 eV are shown in Fig. 3 panel (a) with a comparison to the measured CA and TA component spectra (see the next section for component extraction). The simulations reproduce accurately the experimentally observed shift of the maximum of peak A to higher energy in the course of the dimerization, but not the intensity decrease. For this reason, the interpretations outlined below remain somewhat tentative. The mismatch in the intensity behaviour might occur, because in the simulation, only the dipole excitations are accounted for, whereas in the experiment, also nondipole excitations are present due to significantly nonzero momentum transfer. The normalizations of the spectra are not comparable, as the simulations do not perform accurately with higher-energy excitations, which is also the reason for showing the spectra only up to 291 eV. Slight differences between the experiment and the simulation are also expected because the simulation is performed with optimized geometries of isolated molecules, whereas in the experiment, the samples are in the crystalline form.

Bottom Line: We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects.The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light.Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Helsinki, Finland.

ABSTRACT
A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale. We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects. From the time-resolved spectra, we extracted component spectra and time-dependent weights corresponding to CA and TA. The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light. We also utilized the ability of NRIXS for direct tomography with chemical-bond contrast to image the spatial progress of the reactions in the sample crystal. Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering.

No MeSH data available.


Related in: MedlinePlus