Scattering of Stark-decelerated OH radicals with rare-gas atoms

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X\,^2\Pi_{3/2}, J=3/2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D$_2$ as a function of the collision energy between $\sim 70$ cm$^{-1}$ and 400~cm$^{-1}$. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on accurate \emph{ab initio} potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [Gilijamse \emph{et al.}, Science {\bf 313}, 1617 (2006)], Ar [Scharfenberg \emph{et al.}, Phys. Chem. Chem. Phys. {\bf 12}, 10660 (2010)], He, and D$_2$ [Kirste \emph{et al.}, Phys. Rev. A {\bf 82}, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.Comment: 10 pages, 5 figure

Hexapole state selection and focusing versus brute force orientation of beam molecules.

The commonly used method of orienting polar molecules in a beam, by state selection and focusing with an electrostatic hexapole lens, is compared with the recently introduced orientation method by means of a strong, homogeneous, electric field, based on second- and higher-order Stark effects. The latter, so-called brute force orientation technique, has proved much more effective than had been assumed until recently, and increasingly so if the beam molecules are rotationally very cold. The properties of both techniques are illustrated by a number of examples. The wider applicability and technically simpler implementation of the brute force orientation technique is offset by the absence of state selection. For the description of the molecular orientational distribution this means that, in general, more parameters are needed than for a molecule selected in a single quantum state