Polarization Effects in Collision-Induced Intramultiplet Mixing forNe**{(2p)5(3p)}+He

High-quality polarized-emission cross sections for the ${\left\{\alpha \right\}}_5=|J=1,M_J〉\to {\left\{\alpha \right\}}_7$ and ${\left\{\alpha \right\}}_5\to {\left\{\alpha \right\}}_4$ transitions in the $\left\{\alpha \right\}=\left\{{\mathrm{}\left(2p\right)\mathrm{}}^5\mathrm{}\right(3p\left)\right\}$ multiplet (lifetime 20 ns) have been measured in a crossed-beam experiment. For the ${\left\{\alpha \right\}}_5\to {\left\{\alpha \right\}}_7$ transition we observe a strong preference for the $\left|M_J\right|=0\mathrm{}$ orientation. The small cross section for the $\left|M_J\right|=1\mathrm{}$ orientation can be understood qualitatively from the model potentials of Hennecart and Masnou-Seeuws by the strong coupling to the ${\left\{\alpha \right\}}_4$ and ${\left\{\alpha \right\}}_6$ states (avoided crossings), which is absent for the $\Omega =\left|M_J\right|=0^{-}$ molecular potentials because of the constraint of reflection symmetry.