Grant for Exploratory Research: Electric Field Induced Orientation of Rotationally Cooled Molecules

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Professor Dudley Herschbach is supported by a Small Grant for Exploratory Research from the Experimental Physical Chemistry Program to study molecular orientation in cold molecular beams by the application of strong electric fields. These measurements provide a new method to address questions concerning the importance of relative orientation between reacting molecules and the influence which molecular orientation has on chemical reactivity. Polar molecules with a three-fold or higher axis of symmetry in certain rotational states will precess in an electric field rather than tumble. The dipole moment therefore does not average out for such states, so an electric field can exert a torque which produces substantial orientation. Orientation by an electric field has been considered quite impractical for less symmetrical molecules. The rotational motion of diatomic, linear, or asymmetric top molecules averages out the dipole moment in first-order, so the interaction with an electric field is much weaker. Dr. Herschbach has performed feasibility calculations which show, however, that even in these cases only relatively modest Stark fields of 60,000 volts/cm are required to orient the lowest rotational states of linear molecules such as ICN when they are cooled to 2 degrees Kelvin in a molecular beam. This prediction, which Herschbach hopes to verify experimentally, would have an enormous impact on the whole field of reaction dynamics. It would provide an important new capability to study orientation effects in colliding molecular beams which would be achievable at easily attainable experimental conditions.