3 years ago

Ultrafast x-ray-induced nuclear dynamics in diatomic molecules using femtosecond x-ray/x-ray pump-probe spectroscopy.

M. Bucher, A. A. Lutman, D. Rolles, K. R. Ferguson, C. Bostedt, B. Krassig, S. H. Southworth, A. Rudenko, C. Bomme, C. S. Lehmann, T. Gorkhover, B. Erk, A. Marinelli, A. Picón, D. Ray, E. P. Kanter, P. J. Ho, S. T. Pratt, L. Young, D. Moonshiram, A. M. March, J. Krzywinski, N. Berrah, G. Doumy, T. Osipov

The capability of generating two intense, femtosecond x-ray pulses with controlled time delay opens the possibility of performing time-resolved experiments for x-ray induced phenomena. We have applied this capability to study the photoinduced dynamics in diatomic molecules. In molecules composed of low-Z elements, \textit{K}-shell ionization creates a core-hole state in which the main decay mode is an Auger process involving two electrons in the valence shell. After Auger decay, the nuclear wavepackets of the transient two-valence-hole states continue evolving on the femtosecond timescale, leading either to separated atomic ions or long-lived quasi-bound states. By using an x-ray pump and an x-ray probe pulse tuned above the \textit{K}-shell ionization threshold of the nitrogen molecule, we are able to observe ion dissociation in progress by measuring the time-dependent kinetic energy releases of different breakup channels. We simulated the measurements on N$_2$ with a molecular dynamics model that accounts for \textit{K}-shell ionization, Auger decay, and the time evolution of the nuclear wavepackets. In addition to explaining the time-dependent feature in the measured kinetic energy release distributions from the dissociative states, the simulation also reveals the contributions of quasi-bound states.

Publisher URL: http://arxiv.org/abs/1801.03092

DOI: arXiv:1801.03092v1

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