  We study the role of configuration mixing in the heavier even-even isotopes
of Argon. We begin by limiting the configurations of the even-even Ar isotopes
to $(d_{3/2}^2)_{\pi}$ $(f_{7/2}^n)_{\nu}$. There, due to the particular
location in this shell model space of $^{40}$Ar and $^{44}$Ar, we find that the
spectra, B(E2)'s and magnetic moments of these two nuclei are identical. Any
deviation from this equality is direct evidence of configuration mixing. In a
larger shell model space there are significant differences between these two
nuclei, with $^{44}$Ar being more collective. We also consider other even-even
isotopes of Argon and study how their nuclear structure effects evolve with N.
We compare in the full 0$\hbar \omega$ space $(sd)_{\pi}$ $(fp)_{\nu}$ the
results of calculations with the WBT interaction and with the newer SDPF,
denoted SDPF-U, interaction.
