Infrared Absorption Wavelengths for Solid LiH and LiD

The infrared absorption spectrum of thin films of LiH and LiD was obtained at room temperature for the region 12.5-25 {μ}. The primary feature of the spectrum is a broad but definite absorption peak which occurs at 17.0 {μ} for LiH and at 22.4 {μ} for LiD. The observed ratio of the wavelengths is 1.32±{}0.02, in excellent accord with the ratio of the square root of the reduced masses, 1.33. This agreement is a confirmation of the elementary Born theory of lattice vibrations.