Schematic of the velocity map imaging spectrometer used to detect F+ and Br+ ions. For illustrative purposes, the regions on the detector screen where F+ (Br+) ions are expected to hit for perfectly aligned molecules, at equilibrium, are marked in yellow (black). The images behind the detector are experimental data recorded 2 ps after the kick pulse. The polarization state of the YAG (alignment) pulse (λ = 1064 nm, τFWHM = 10 ns, IYAG = 6 × 1011 W/cm2) and the kick pulse (800 nm, 200 fs, Ikick = 2 × 1013 W/cm2) are also displayed.
Vertical profiles of the molecular beam measured by recording the C+ signal as a function of the vertical position of the probe beam focus. The experimental data are shown by black squares (deflector off, 0 kV) and red circles (deflector on, 10 kV). The red arrow at Y = 1.3 mm indicates the position of the laser foci used to acquire ion images of the deflected molecules.
F+ (panels (a) and (c)) and Br+ (panels (b) and (d)) ion images obtained as a function of the kick-probe time delay indicated in ps above each column of panels. Panels (a) and (b) and (c) and (d) were obtained using a linearly polarized probe pulse being perpendicular to (parallel with) the detector. The delay of the probe pulse (λ = 800 nm, τFWHM = 30 fs, Iprobe = 3 × 1014 W/cm2) with respect to the kick pulse (λ = 800 nm, τFWHM = 200 fs, Ikick = 2 × 1013 W/cm2) is given by the numbers on the top of the vertical panels.
(a) Time-dependence of the dihedral angle (blue triangles) following the kick pulse, obtained by adding the orientation of the F-phenyl-ring (black squares) and the orientation of the Br-phenyl-ring with respect to the SMPA—see text for details. (b) Sketch of the molecular structure as seen in end view. The SMPA of the molecule and the extracted angles are marked on the drawing.
F+ (a) and Br+ (b) ion images obtained at long (t ⩾ 3 ps) kick-probe time delays obtained using a probe pulse linearly polarized perpendicular to the detector. The delay of the probe pulse (λ = 800 nm, τFWHM = 30 fs, Iprobe = 3 × 1014 W/cm2) with respect to the kick pulse (λ = 800 nm, τFWHM = 200 fs, Ikick = 2 × 1013 W/cm2) is given by the numbers on the top of the vertical panels.
Time dependence of the planar alignment of the individual phenyl-rings. The ⟨cos 2α2D ⟩ values are calculated from rotated angular distributions to remove the effect of the torsion (see text for details). Black squares (red circles) correspond to the confinement of the F-phenyl-ring (Br-phenyl- ring).
The autovariance mapping principle illustrated for F+ fragments produced by coulomb explosion of laser aligned DFDBrCNBph. From the autovariance map seen on the right, it is possible to extract correlation information between the ejection angle of the F+ ions. The blue arrows indicate the steps in the data acquisition and data processing leading to the production of autovariance maps.
Autovariance maps for F+ (upper panels) and Br+ ions (lower panels) at kick-probe time delays of 2 ps (left column) and 10 ps (right column). To smoothen out small fluctuations, the data have been binned in steps of 5°. Also the large signal, due to autocorrelation, along the diagonal of the maps, has been set to zero to reveal the less intense correlations in the autovariance map.
Comparison: Blue triangles—experimental results, dashed blue line—theoretical calculation on DFDBrBPh shifted by −0.9° to match the dihedral angle of DFDBrCNBPh at equilibrium.
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