2019, Karamatskos, Evangelos T., Raabe, Sebastian, Mullins, Terry, Trabattoni, Andrea, Stammer, Philipp, Goldsztejn, Gildas, Johansen, Rasmus R., Długołecki, Karol, Stapelfeldt, Henrik, Vrakking, Marc J. J., Trippel, Sebastian, Rouzée, Arnaud, Küpper, Jochen

Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. Here we present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, 〈cos2θ2D〉 = 0.96 (〈cos2θ〉 = 0.94) is achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schrödinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalises the observed very high degree of alignment.

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.