Fringe-field effects on the time evolution of pendular states

The interaction of the permanent electric dipole moment of a polar molecule with a strong static electric field can create oriented rotational wave packets, which are termed pendular states. Molecules traveling in a molecular beam experience a fringing field due to the edges of the conducting plates which create the electric field as a slowly varying time-dependent perturbation. Since Stark energies of some asymmetric-top molecules present numerous avoided crossings as a function of field strength, the time evolution of rotational wave functions for molecules entering the field is complex. We have studied, by solving the time-dependent Schrödinger equation, the dynamics caused by selected avoided crossings, and the time evolution of the orientation corresponding to 24 rotational wave functions, for the near-prolate asymmetric-top iodobenzene. Implications for the population distribution of molecules in the electric field and for experimental schemes to decelerate molecules are discussed. © 2000 The American Physical Society.