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Optical absorption spectra of ruby and periclase at high shock pressures

Gaffney, Edward S. and Ahrens, Thomas J. (1973) Optical absorption spectra of ruby and periclase at high shock pressures. Journal of Geophysical Research, 78 (26). pp. 5942-5953. ISSN 0148-0227. doi:10.1029/JB078i026p05942.

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A spectrographic system is described that is capable of measuring optical absorption spectra in solids to shock pressures of several hundred kilobars. The system utilized light from a ‘point’ source at about 60,000°K. Spectra have a resolution of about 40 A and cover the visible range. With a streak camera, time resolution of about 75 nsec can be obtained. The spectrum of MgO is observed to remain featureless at 450 kb and upon unloading from this pressure. The color centers observed in shock-recovered material must result from either higher pressures or other processes. The optical absorption spectra of ruby under shock compressions of almost 15% have been measured in the range 375–600 nm. Below the elastic limit the large anisotropic strains are evident from the splitting of the ^4A_2 → ^4T_2 (F) absorption band by 3730 cm^(−1). Above the elastic limit this splitting is not resolved (but must be less than 800 cm^(−1)), indicating considerable loss of shear strength in such cases. Above the Hugoniot elastic limit up to pressures of 530 kb (15% volume compression) the measured value of the crystal field parameter agrees, within experimental error, with the value calculated from a point charge model (Dq α r^(−5)) if the local compressibility is equal to the bulk compressibility. This result agrees with Stephens and Prickamer's absorption data up to 150 kb and suggests that the point charge model is useful in predicting crystal field effects in mantle minerals, especially those having similar oxygen anion packings such as corundum.

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Additional Information:Copyright 1973 by the American Geophysical Union. (Received November 13, 1972; revised April 13, 1973.) Many helpful suggestions in experiment design were made by H. F. Swift and E. J. Bunker. We appreciate the experimental help of J. Lower, D. Johnson, and H. Richeson. Conversations with G. Rossman, T. J. Shankland, and R. Vaughn were most helpful and are gratefully acknowledged. This work was supported by the National Science Foundation under grant NSF GA 21396. Contribution 2232, Division of Geological and Planetary Sciences, California Institute of Technology.
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NSFGA 21396
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Caltech Division of Geological and Planetary Sciences2232
Issue or Number:26
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Official Citation:Gaffney, E. S., and T. J. Ahrens (1973), Optical absorption spectra of ruby and periclase at high shock pressures, J. Geophys. Res., 78(26), 5942–5953, doi:10.1029/JB078i026p05942.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51402
Deposited By: George Porter
Deposited On:07 Nov 2014 15:59
Last Modified:10 Nov 2021 19:10

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