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Improved sliced velocity map imaging apparatus optimized for H photofragments
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Image of FIG. 1.
FIG. 1.

Minimal SVMI system with 3-electrode ion optics and its performance characteristics under simultaneous TOF and radial focusing conditions: (a) cross-section diagram, (b) image radius for 1 eV ions, (c) relative radial blurring in the KE scale, (d) relative TOF blurring. (The distance between the ionization region and the second electrode was chosen as the independent parameter for plotting. E 0 was fixed at 58 V/cm for 50 ns TOF stretching. Total TOF length L = 60 cm.)

Image of FIG. 2.
FIG. 2.

Cross-section of the ion optics arrangement with illustration of electrostatic potentials and ion trajectories for the extreme operating conditions: (a) lower KE limit (K max = 0.163 eV; L 0 = 40 mm, L 1 = 50 mm, V 0 = 320 V, V 1 = 231.1 V, V L = 0); (b) upper KE limit (K max = 6.75 eV; L 0 = 75 mm, L 1 = 55 mm, V 0 = 3000 V, V 1 = 1891 V, V L = −6600 V). In both cases Δτmax ≈ 50 ns. Trajectories correspond to ions with initial KEs equal to K max (red), 0.4K max (green) and 0.1K max (blue); see text for details. Equipotential contours are drawn in red for positive potentials (with 10 V steps in (a) and 100 V in (b)) and blue for negative (with 500 V steps).

Image of FIG. 3.
FIG. 3.

Pareto-optimal results of numerical simulations plotted as functions of the magnification index M and the effective accelerator lengths L 0 and L 1 (in mm): relative overall kinetic energy (ΔK) and total TOF (Δt) resolutions, and the ratio of the voltages applied to the additional lens (V L ) and the back of the accelerator (V 0). (Both columns show the same set of data, but colored according to L 0 (left) or L 1 (right) values.)

Image of FIG. 4.
FIG. 4.

Distribution of O+ ions in the photoinitiated reaction at ν ≈ 44 444 cm−1. (a) Raw sliced velocity map image (with vertical laser polarization) recorded without the additional lens. (b) Comparison of KEDs extracted from SVMI data recorded with and without the lens.

Image of FIG. 5.
FIG. 5.

Distributions of H fragments in photodissociation of HBr and H2S. (a) and (b) show raw SVMI data for and processes, specifically (only one half of each symmetric image is shown). (c) KEDs extracted from these data.

Image of FIG. 6.
FIG. 6.

H fragment distribution in CH2OH dissociation after electronic excitation at ν ≈ 27 420 cm−1vac = 3Ly-α). (a) Raw full-projection VMI data. (b) Raw SVMI data. (c) Comparison of KEDs extracted from these data. Notice the significantly worse signal-to-noise ratio in the full-projection reconstruction despite longer data accumulation.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Improved sliced velocity map imaging apparatus optimized for H photofragments