Surface three-dimensional velocity map imaging: A new technique for the study of photodesorption dynamics
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)
The authors describe the application of a combination of velocity map imaging and time-of-flight (TOF) techniques to obtain three-dimensional velocity distributions for surface photodesorption. They have established a systematic alignment procedure to achieve correct and reproducible experimental conditions. It includes four steps: (1) optimization of the velocity map imaging ion optics' voltages to achieve optimum velocity map imaging conditions; (2) alignment of the surface normal with the symmetry axis (ion flight axis) of the ion optics; (3) determination of TOF distance between the surface and the ionizing laser beam; (4) alignment of the position of the ionizing laser beam with respect to the ion optics. They applied this set of alignment procedures and then measured Br({sup 2}P{sub 3/2}) (Br) and Br({sup 2}P{sub 1/2}) (Br*) atoms photodesorbing from a single crystal of KBr after exposure to 193 nm light. They analyzed the velocity flux and energy flux distributions for motion normal to the surface. The Br* normal energy distribution shows two clearly resolved peaks at approximately 0.017 and 0.39 eV, respectively. The former is slightly faster than expected for thermal desorption at the surface temperature and the latter is hyperthermal. The Br normal energy distribution shows a single broad peak that is likely composed of two hyperthermal components. The capability that surface three-dimensional velocity map imaging provides for measuring state-specific velocity distributions in all three dimensions separately and simultaneously for the products of surface photodesorption or surface reactions holds great promise to contribute to our understanding of these processes.
- OSTI ID:
- 22051134
- Journal Information:
- Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films, Vol. 28, Issue 4; Other Information: (c) 2010 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1553-1813
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALIGNMENT
BROMINE
DESORPTION
ENERGY SPECTRA
EV RANGE
LASER RADIATION
MAPPING
MONOCRYSTALS
PHOTON BEAMS
POTASSIUM BROMIDES
SURFACES
THREE-DIMENSIONAL CALCULATIONS
TIME-OF-FLIGHT METHOD
VELOCITY
VISIBLE RADIATION