Isospin Mixing of4−Particle-Hole States inO16

Transitions to ($4^{-}$,$T=0\mathrm{}$) states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 17.79 and 19.80 MeV are found to be strongly asymmetric in ${\pi }^{+}$ vs ${\pi }^{-}$ inelastic scattering; in contrast, the ${\pi }^{+}$ and ${\pi }^{-}$ cross sections for the ($4^{-}$, $T=1\mathrm{}$) state at 18.99 MeV are equal. Three-state isospin mixing is proposed as an explanation. Off-diagonal charge-dependent mixing matrix elements of - 147±25 and - 99±17 keV are obtained.