Improved sliced velocity map imaging apparatus optimized for H photofragments

Journal Article · Sun Apr 14 04:00:00 EDT 2013 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4798929· OSTI ID:22105472

Ryazanov, Mikhail; Reisler, Hanna ^[1]

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1. Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482 (United States)

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud. Time slices of {approx}5 ns out of a cloud stretched to Greater-Than-Or-Slanted-Equal-To 50 ns are used. An accelerator region with variable dimensions (using multiple electrodes) is employed for better optimization of radial and temporal space focusing characteristics at each magnification level. The implemented system was successfully tested by recording images of H fragments from the photodissociation of HBr, H{sub 2}S, and the CH{sub 2}OH radical, with kinetic energies ranging from <0.4 eV to >3 eV. It demonstrated KE resolution Less-Than-Or-Equivalent-To 1%-2%, similar to that obtained in traditional velocity map imaging followed by reconstruction, and to KE resolution achieved previously in SVMI of heavier products. We expect it to perform just as well up to at least 6 eV of kinetic energy. The tests showed that numerical simulations of the electric fields and ion trajectories in the system, used for optimization of the design and operating parameters, provide an accurate and reliable description of all aspects of system performance. This offers the advantage of selecting the best operating conditions in each measurement without the need for additional calibration experiments.

• OSTI ID: 22105472
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 14 Vol. 138; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
43 PARTICLE ACCELERATORS
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
74 ATOMIC AND MOLECULAR PHYSICS
COMPUTERIZED SIMULATION
CONTROL
DISSOCIATION
ELECTRIC FIELDS
ELECTROSTATIC LENSES
EV RANGE
HYDROBROMIC ACID
HYDROGEN
IONS
KINETIC ENERGY
MAPS
NUMERICAL ANALYSIS
OPTIMIZATION
PHOTOLYSIS
PHOTON-MOLECULE COLLISIONS
RESOLUTION
VELOCITY