2020, Forbes, Ruaridh, Allum, Felix, Bari, Sadia, Boll, Rebecca, Borne, Kurtis, Brouard, Mark, Bucksbaum, Philip H., Ekanayake, Nagitha, Erk, Benjamin, Howard, Andrew J., Johnsson, Per, Lee, Jason W.L., Manschwetus, Bastian, Mason, Robert, Passow, Christopher, Peschel, Jasper, Rivas, Daniel E., Rörig, Aljoscha, Rouzée, Arnaud, Vallance, Claire, Ziaee, Farzaneh, Rolles, Daniel, Burt, Michael

The predissociation dynamics of the 6s (B2E) Rydberg state of gas-phase CH3I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous © 2020 The Author(s). Published by IOP Publishing Ltd Printed in the UK

2017-04-10, Savelyev, Evgeny, Boll, Rebecca, Bomme, Cédric, Schirmel, Nora, Redlin, Harald, Erk, Benjamin, Düsterer, Stefan, Müller, Erland, Höppner, Hauke, Toleikis, Sven, Müller, Jost, Kristin Czwalinna, Marie, Treusch, Rolf, Kierspel, Thomas, Mullins, Terence, Trippel, Sebastian, Wiese, Joss, Küpper, Jochen, Brauβe, Felix, Krecinic, Faruk, Rouzée, Arnaud, Rudawski, Piotr, Johnsson, Per, Amini, Kasra, Lauer, Alexandra, Burt, Michael, Brouard, Mark, Christensen, Lauge, Thøgersen, Jan, Stapelfeldt, Henrik, Berrah, Nora, Müller, Maria, Ulmer, Anatoli, Techert, Simone, Rudenko, Artem, Rolles, Daniel

In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C6H3F2I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. We discuss in detail the necessary data analysis steps and describe the origin of the time-dependent effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.

2018, Amini, Kasra, Savelyev, Evgeny, Brauße, Felix, Berrah, Nora, Bomme, Cédric, Brouard, Mark, Burt, Michael, Christensen, Lauge, Düsterer, Stefan, Erk, Benjamin, Höppner, Hauke, Kierspel, Thomas, Krecinic, Faruk, Lauer, Alexandra, Lee, Jason W. L., Müller, Maria, Müller, Erland, Mullins, Terence, Redlin, Harald, Schirmel, Nora, Thøgersen, Jan, Techert, Simone, Toleikis, Sven, Treusch, Rolf, Trippel, Sebastian, Ulmer, Anatoli, Vallance, Claire, Wiese, Joss, Johnsson, Per, Küpper, Jochen, Rudenko, Artem, Rouzée, Arnaud, Stapelfeldt, Henrik, Rolles, Daniel, Boll, Rebecca

We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon-iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.