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.
Highlights
NRIXS is a versatile technique for probing excitations of various energy ranges, from vibrational to valence- or core-level electronic excitations[12,13,14]
The time-evolution of the carbon core-electron excitation spectra measured from the crystalline samples of α -trans-cinnamic and α -truxillic acid are displayed in Fig. 2 panels (a) and (b), respectively
The value of the Avrami exponent near one in our experiment suggests that the reaction may proceed more homogeneously with the rate being linearly dependent on the reactant concentration
Summary
NRIXS is a versatile technique for probing excitations of various energy ranges, from vibrational to valence- or core-level electronic excitations[12,13,14]. We report our novel time-resolved inelastic X-ray scattering study of a solid-state topochemical reaction: The X-ray induced dimerization of α -trans-cinnamic acid (CA) to α -truxillic acid (TA). To follow the spatial progress of the dimerization, we have utilized the ability of NRIXS to direct tomography with a chemical-bond contrast[15]. As a time-resolved imaging experiment on a chemical reaction, this study is an important step towards the realization of the full potential of NRIXS. We present the evolution of the carbon core-electron excitation spectrum from the CA sample as a function of time and discuss the observed dimerization effect in the spectrum with the help of simulations and reference TA spectra. We discuss the reaction kinetics and their differences compared to traditional UV-light induced dimerization
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