Large Rotational Polarization Observed forH2,D2, and HD Scattered from LiF(001)

Molecular angular-momentum polarization produced in gas-surface collisions is investigated by the magnetic field effect on a Knudsen flow. The effects for ${\mathrm{H}}_2$ isotopes scattered by LiF(001) surfaces are found to be 2 to 3 orders of magnitude larger than previously observed for metal surfaces. This is attributed to the large corrugation of the LiF crystal face, since the polarization type involved is produced by in-plane forces. Both first- and second-rank polarizations ("orientation" and "alignment") are observed, the production matrix elements being of order ${10}^{-1\mathrm{}}$ to ${10}^{-2\mathrm{}}$.