Site-selective-induced isomerization of formamide

Abstract

The new capacity of X-ray free-electron laser (XFEL) facilities to produce multi-color Xray femtosecond pulses paves the way to explore ultrafast phenomena in matter induced by X-ray photons. In the present study, we exploit the site selectivity and the high temporal resolution of a two-color X-ray femtosecond pump-probe sequence to investigate the isomerization of formamide. The pump pulse excites a particular atomic site in the molecule, while the probe pulse captures changes in the chemical environment at a remote atomic site. The response of the system is found to strongly depends on the nature of the excited site, and the core excitation provides a selective control on chemical bond breaking. In particular, we show that the N1s → π * transition favors the isomerization reaction in formamide and demonstrate the possibility to observe in real time the hydrogen migration by measuring the time-dependent chemical shifts with the X-ray probe pulse. This work opens a unique perspective for X-rayinduced photochemistry at XFEL facilities.

NEXAFS and MS-AES spectroscopy of the C 1s and Cl 2p excitation and ionization of chlorobenzene: Production of dicationic species

“…31 Recent investigations of the sitespecificity in small molecules such as formamide, XeF 2 and acetylene dication were conducted at X-ray free-electron laser facilities using the high temporal resolution of X-ray pump-probe spectroscopy, where transient dynamics could be followed through the intermediate states. [16][17][18] Here, we have quantitatively evaluated site-specificity aspects of singly and doubly-charged photoions, by a combination of NEXAFS, coincident AES and TOF-MS. The prediction of hetero-site-specificity in species formation remains challenging.…”

From synchrotrons for XFELs: the soft x-ray near-edge spectrum of the ESCA molecule

“…These methods were benchmarked on other simple molecules (NH 3 , H 2 CO, CO 2 ) and are thought to be generalizable. While most time-resolved NEXAFS spectra have been used to interpret dynamics due to optical/UV excitation of valence states [26,16], NEXAFS can also provide fingerprints to follow inner-shell-initiated molecular dynamics -a discipline which is now feasible and a natural extension to x-ray pump/probe methods at XFELs [17,89,90,91,92]. Ethyl trifluoroacetate has already proven itself a model for ESCA (electron spectroscopy for chemical analysis), and, now extends its reach to advance theoretical methods to describe complex innershell photoabsorption spectra.…”

Atomic, molecular and optical physics applications of longitudinally coherent and narrow bandwidth Free-Electron Lasers

“…Also, the generation of soft X-ray two-colour double FEL pulses, especially attosecond/few-femtosecond double pulses (Duris et al, 2020), are atractrive and stimulated renewed interest in time-resolved XPS. Oberli et al (2019), for example, showed that the N 1s → π * transition can induce an isomerization reaction in formamide and that it is possible to observe in real time hydrogen migration by time-resolved XPS, measuring the chemical shifts with the X-ray probe pulse.…”