Alignment ofNe8+nP1states produced by collisions ofNe9+withH2at 4 keV/amu

Relative intensities and polarization rates of $n{}_{}{}^1{}_{}{}^{}P\to 1{}_{}{}^1{}_{}{}^{}S$ heliumlike Lyman x rays emitted in collisions of 4-keV/amu ${\mathrm{Ne}}^{9+}$ ions with ${\mathrm{H}}_2$ have been measured. Our experimental results are discussed in connection with molecular calculations for the near-system ${\mathrm{F}}^{9+}$+H. High polarization rates (∼60%) are measured for direct x rays, indicating a strong predominance of $m=0\mathrm{}$ substates in final $n{}_{}{}^1{}_{}{}^{}P$ states, in agreement with the theory. This shows the existence of a strong rotational coupling in the molecular frame. The difference of polarization observed for the $2P\to 1S$ and $3P\to 1S$ x rays may originate from a higher anisotropy of the low-angular-momentum states with respect to the high ones, as predicted by the theory.