Field-Free Orientation of Molecules

We consider impulsive excitation of a linear polar molecule by a plane polarized electromagnetic “half-cycle” pulse in the terahertz range. A rotational wave packet is created with angular momentum states of different parity. The time evolution of the wave packet corresponds to alternating molecular orientations with respect to the polarization axis of the field. This field-free time-dependent orientation of the molecule is computationally demonstrated, also at finite temperatures, with LiH and NaI as examples.