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Real-time data acquisition for gas electron diffraction

1984; American Institute of Physics; Volume: 55; Issue: 10 Linguagem: Inglês

10.1063/1.1137624

1527-2400

John D. Ewbank, Lothar Schäfer, David W. Paul, O. Joel Benston, John C. Lennox,

Spectroscopy and Laser Applications

An instrument for gas electron diffraction (GED) studies is described which eliminates the photographic intermediary and sector device which are currently used almost universally in molecular structure determinations using GED. Specifically, the scattered electrons are detected by a fluorescent screen which is optically coupled to a custom multichannel analyzer (EG&G model 1412 photodiode array detector and model 1218 controller, combined with a MINC-DEC LSI 11/23 computer). Rapid operation not only eliminates photographic film development and densitometry, but also allows for repeated measurements to be easily made. Dynamic data acquisition provides for virtually steady-state conditions in the experimental environment, minimizing systematic errors and providing a means for instrument control. The design has been completed to the extent that small angle scattering data are now readily recorded in this novel way. The data range accessible in the current configuration (maximum s values of approximately 20–25 Å−1) is smaller than that normally used in structural GED work (maximum s values of typically 30–40 Å−1), but useful structural information can be derived from it. To demonstrate the currently achieved resolution, several test molecules have been modeled based on this novel data recording technique, and results are compared to those found in the literature. The success of the current scheme brings to mind other configurations to be tested, including direct exposure of the photodiode array detector to the scattered electrons. Powder diffraction data are also readily recorded on the new instrument. It is expected that the instrument will be particulary useful in time-resolved studies of dynamical processes, in the investigation of transient species, and in practical applications, for example, for analytical purposes.