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.