Absorption of NaCl, KCl and KI in the Far Ultraviolet

With a normal incidence concave grating vacuum spectrograph with a hot spark for a light source and oiled photographic films, qualitative absorption curves for NaCl, KCl, and KI between 190A and 1550A have been obtained. The absorbing film of the alkali halide was distilled directly onto the ruled surface of the grating. The positions of maximum absorption as read from the three curves presented are: for NaCl, 655A, 535A, 350A, and 890A; for KCl, 705A, 530A, 320A, and 1120A; for KI, 825A, 625A, and 510A, all accurate to 6 percent. These results are at variance with early theoretical extrapolations from the known form of the dispersion curves for rocksalt and silvite in the near infrared.