Zum inneren lichtelektrischen Effekt (Quantensprungabsorption) im Alkalimetall Kalium
The results of new measurements of the optical constantsn andk of the alkali metalK, performed in ultrahigh vacuum on mirrorlike surfaces free of any contamination and distortion in the wavelength region from 0·365 μ to 2 μ at temperatures between −183° C and +85° C permit to separate the absorption due to interband transitions (photoexcitation of valency electrons) from the “classical absorption” solely considered in Drude's theory of the optical constants of metals. Thus, it is possible to determine the “internal photoelectric effect” of the alkali metal potassium as a function of wavelength, espically its threshold frequency which corresponds to a wavelengthλth=2·1 μ (hνth=0·59 eV).