isotopically deficient
An @I03336@ compound may be designated as isotopically deficient when the isotopic content of one or more elements has been depleted, i.e. when one or more @N04257@ is (are) present in less than a natural ratio.
Blue Book, p. 518 [Terms] [Book]
PAC, 1981, 53, 1887. (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1896 [Terms] [Paper]