Abstract
We report on the measurement of deep inner-shell 2p X-ray photoelectron diffraction (XPD) patterns from laser-aligned I2 molecules using X-ray free-electron laser (XFEL) pulses. The XPD patterns of the I2 molecules, aligned parallel to the polarization vector of the XFEL, were well matched with our theoretical calculations. Further, we propose a criterion for applying our molecular-structure-determination methodology to the experimental XPD data. In turn, we have demonstrated that this approach is a significant step toward the time-resolved imaging of molecular structures.
Highlights
In this Article, we report on I 2p photoelectron angular distributions from both randomly oriented and laser-aligned I2 molecules using X-ray free-electron lasers (XFELs) pulses from the SPring-8 Ångström Compact free-electron LAser (SACLA)
Electrons produced in the interaction region are drawn into the upper velocity-map imaging spectrometers (VMIs), while ions are drawn into the lower VMI: the former records two-dimensional (2D) photoelectron diffraction images, and the latter records 2D fragment-ion images to monitor the degree of alignment of the I2 molecules in real time
The present X-ray photoelectron diffraction (XPD) pattern is strongly affected by the degree of alignment for the sample molecules, as described above
Summary
In this Article, we report on I 2p photoelectron angular distributions from both randomly oriented and laser-aligned I2 molecules using XFEL pulses from the SPring-8 Ångström Compact free-electron LAser (SACLA). We selected a kinetic energy of 140 eV for the 2p photoelectrons, which ensures that in an aligned molecule the XPD pattern is dominated by a photoelectron wave emitted from an emitter atom and a scattered wave from a neighboring atom, exhibiting the interference structure between the two electron waves (see Fig. 1)[13,24,25,26]. This situation, in which two electron waves interfere depending on both the internuclear distance and electron energy (in other words, the electron de Broglie wavelength), is similar to that in Young’s double-slit experiments. We have confirmed that this approach is a critical step toward the time-resolved imaging of molecular structures
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