Isotope shift of 667.7mm transition in atomic argon.

Doppler-free optogalvonic measurements of the 667.7mm 4s [3/2] (1) to 4p [1/2](o) transition in (36.38.40)Ar have yielded values for the isotope shifts, field shifts and delta. The field shift, calibrated with muonic x-ray data, demonstrate a significantly larger delta for (38-40)Ar, (.17 fm (2)) then for (36-38)Ar (.07 fm(2)) consistent with similar data for K and Ca crossing the 1f(1/2) magic neutron number N = 20.