= Pendular state
A <pendular state> is a field-dressed rotational <quantum state> in which a <molecule>'s orientation is concentrated near a preferred direction, resembling small angular librations of a pendulum. It arises when the orienting or aligning field interaction competes strongly with <rotational kinetic energy>.
A permanent dipole in a static <electric field> has an interaction proportional to $-\cos\theta$, which distinguishes opposite directions. An anisotropic induced-polarization interaction often depends on $-\cos^2\theta$, aligning an axis without necessarily orienting its two ends. The field strength and <rotational constant> determine whether a weak-field perturbation treatment is adequate.
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