Abstract
Single-shot time-of-flight spectra for Coulomb explosion of N2 and I2 molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N4+–N5+ channel for nitrogen and up to the I8+–I9+ channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N2 ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
Highlights
Over the last few years, accelerator-based free-electron lasers (FELs) have emerged as new, large-scale user facilities, providing unprecedented XUV/x-ray fluences and intensities [1,2,3,4]
Circumventing the above-mentioned drawbacks of ion– ion coincidence schemes and velocity map imaging, we present in this paper, as a third method, an improved covariance mapping technique, proposed some time ago [20, 21] and implemented recently at the Free Electron LASer in Hamburg (FLASH) FEL in Hamburg, where we have used intense FEL pulses at 91 eV (13.7 nm) to observe dissociative ionization and Coulomb explosion of two diatomic molecules, N2 and I2
Recording single-shot ion TOF spectra for the ionization of N2 and I2 molecules by intense XUV pulses at the FLASH FEL and a subsequent analysis of the data using a partial covariance mapping technique allows the extraction of momentum distributions for all significant Coulomb explosion channels
Summary
Over the last few years, accelerator-based free-electron lasers (FELs) have emerged as new, large-scale user facilities, providing unprecedented XUV/x-ray fluences and intensities [1,2,3,4]. The considerable scientific and financial investment that underlies these developments is driven by applications in structural biology, where the possibility of determining the structure of tiny crystals or even non-crystalline materials. 46 (2013) 164028 such as single macro-molecules and cells offers a promise substantially beyond the opportunities offered by contemporary synchrotron light sources [5, 6]. Initial results that have been obtained at the Linac Coherent Light Source at Stanford have already provided first glimpses of the potential of these techniques [7,8,9,10]
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