Overview of the spectrometer and the target injection setup in the CAMP chamber  used to perform coincident ion momentum spectroscopy on small organic molecules ionized with an x-ray FEL
Figure 1. Overview of the spectrometer and the target injection setup in the CAMP chamber  used to perform coincident ion momentum spectroscopy on small organic molecules ionized with an x-ray FEL. The molecules are injected into the vacuum in a continuous supersonic molecular beam and are ionized by the focused XFEL beam inside a spectrometer that allows coincident 3D-momentum-resolved detection of fragment ions emitted in the full 4π solid angle on a delay line detector (see text for details). Inset: sketch of the geometries of methylselenol and ethylselenol molecules.
The ionization and fragmentation of two selenium containing hydrocarbon molecules, methylselenol (CH3SeH) and ethylselenol (C2H5SeH), by intense (>1017 W cm−2) 5 fs x-ray pulses with photon energies of 1.7 and 2 keV has been studied by means of coincident ion momentum spectroscopy. Measuring charge states and ion kinetic energies, we find signatures of charge redistribution within the molecular environment. Furthermore, by analyzing fragment ion angular correlations, we can determine the laboratory-frame orientation of individual molecules and thus investigate the fragmentation dynamics in the molecular frame. This allows distinguishing protons originating from different molecular sites along with identifying the reaction channels that lead to their emission.