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

达德利·赫施巴赫教授得到了实验物理化学计划的一小笔探索性研究补助金的支持，该计划通过应用强电场来研究冷分子束中的分子取向。这些测量提供了一种新的方法来解决有关反应分子之间相对取向的重要性以及分子取向对化学反应活性的影响的问题。在某些旋转态中具有三重或更高对称轴的极性分子将在电场中前进，而不是翻滚。因此，偶极矩对于这种状态并不是平均的，所以电场可以施加一个扭矩，从而产生实质性的取向。人们认为，对于对称性较差的分子来说，通过电场来定向是非常不现实的。双原子、线性或不对称顶层分子的旋转运动在一阶中平均偶极矩，因此与电场的相互作用要弱得多。然而，赫施巴赫博士进行的可行性计算表明，即使在这些情况下，当ICN等线性分子在分子束中冷却到2开尔文时，也只需要相对较小的60,000伏/厘米的斯塔克场来定向它们的最低转动状态。赫施巴赫希望通过实验验证这一预测，这将对整个反应动力学领域产生巨大影响。这将为研究分子束碰撞中的取向效应提供一个重要的新能力，这将在容易获得的实验条件下实现。

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.