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An investigation of the infra-red spectrum of magnesium oxide has been carried out in the range up to 25.5 μ, both in reflection and transmission. The eigen-frequency is found to be at 17.5 ± 0.3 μ and four subsidiary maxima have been found in transmission. The results of Barnes, Brattain and Seitz in the range up to 15.6 μ have not been confirmed and no detailed fine structure has been found. The reflection spectrum of magnesium oxide has been fully investigated up to 25.5 μ, and a broad reflection maximum has been found extending from 17 μ to 21 μ, with subsidiary maxima at 14.02 μ and 23.8 μ.
J C Willmott (1950) studied this question.