Direct observation of the steric effect in chemical reactions by controlling the orientation at transition state

通过控制OH自由基取向，直接观察了OH + HBr化学反应中的立体效应，阐明了立体各向异性的机理。结果表明，氢氧根o端比h端更有利于HBr的碰撞。理论分析表明，至少有两种机制起作用，使观察到的空间效应。一个是氢氧根o端氢原子的抽离另一个是氢氧根H端氢原子的迁移。用206nm线偏振激光对CO(a)进行对准。这一成功将使我们能够以一种新颖的方式控制过渡态的分子取向。

Direct observation of the steric effect in the OH + HBr chemical reaction was made by controlling the OH radical orientation in order to clarify mechanisms for stereo-anisotropy. We find that the HBr collision at the O-end of OH radical is more favorable than that at the H-end. The theoretical analysis suggested that there are at least two mechanisms play roles to give the observed steric effect. One is the H atom abstraction at the O-end of OH and another is the H atom migration at the H-end of OH. Alignment of CO(a) was performed using a linearly polarized laser at 206nm. This success will allow us to control molecular orientation at transition state in a novel way.