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Lattice bands in AlSb involving interactions of infrared radiation with one, two, three, and four phonons have been observed between 8 and 38 /i. The multiphonon combination bands (summation or difference) can be explained in terms of four characteristic phonons at or near the zone boundary. The corresponding phonon wave numbers are 316, 297, 132, and 65 cm -1 . The interaction of infrared radiation with the transverse optical phonon at the center of the zone results in a single-phonon absorption band and the Reststrahlen reflectivity band. The reflectivity data can be fitted to simple dispersion theory. The fundamental optical frequency from this fit is (9.564zb0.019)Xl0 12 sec -1 (319 cm -1 ). The index of refraction n and extinction coefficient k were calculated as functions of wavelength between 20 and 38 /z using dispersion theory.