  We have investigated the wave-function feature of Rydberg sodium in a uniform
electric field and found that the core-induced interaction of non-hydrogenic
atom in electric field can be directly visualized in the wave-function. As is
well known, the hydrogen atom in electric field can be separated in parabolic
coordinates (\eta, \xi), whose eigen-function can show a clear pattern towards
negative and positive directions corresponding to the so-called red and blue
states without ambiguity, respectively. It can be served as a complete
orthogonal basis set to study the core-induced interaction of non-hydrogenic
atom in electric field. Owing to complete different patterns of the probability
distribution for red and blue states, the interaction can be visualized in the
wave-function directly via superposition. Moreover, the constructive and
destructive interferences between red and blue states are also observed in the
wave-function, explicitly explaining the experimental measurement for the
spectral oscillator strength.
