Centimeter Wave Absorption in Molecular Crystals
Final rept. Jan 1990-Jun 1991
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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Molecular dynamics calculations performed at the University of Nebraska predict that temperature-dependent microwave activity is present in some ionic molecular crystals. This activity is due to the excitation of hindered rotations or thermally activated hopping modes for the molecular ions. Microwave reflectometer measurements performed at the BRL show temperature-dependent microwave losses occur in several ionic molecular crystals at or near the calculated orderdisorder transition temperatures. These measurements, performed from 2 to 20 GHz from room temperature to about 300 deg C on the BRL arch, were made on powder samples of the nitrates and nitrites of potassium, sodium, and other materials. Potassium nitrate displays an interesting temperature dependence with the absorption turning on at about 1200 C, near the calculated orderdisorder transition temperature. Measurements were also performed on selected ionic salts which uniformly show small microwave losses at any of the temperatures measured.
- Atomic and Molecular Physics and Spectroscopy
- Radiofrequency Wave Propagation