It has long been known that there is a conical intersection (CI) between the ground and first excited electronic state in the H₃ system. Its associated geometric phase (GP) effect has been theoretically predicted to exist below the CI since a long time. However, the experimental evidence has not been established yet and its dynamical origin is waiting to be elucidated. Here we report a combined crossed molecular beam and quantum reactive scattering dynamics study of the H+HD → H₂+D reaction at 2.28 eV, which is well below the CI. The GP effect is clearly identified by the observation of distinct oscillations in the differential cross section around the forward direction. Quantum dynamics theory reveals that the GP effect arises from the phase alteration of a small part of the wave function, which corresponds to an unusual roaming-like abstraction pathway, as revealed by quasi-classical trajectory calculations.

早就知道在H ₃系统中，在地面与第一激发电子态之间存在圆锥形交点（CI）。从理论上讲，很长一段时间以来，它的相关几何相位（GP）效应就一直存在于CI之下。但是，实验证据尚未建立，其动力学起源正在等待阐明。在这里，我们报告结合的交叉分子束和H + HD→H _2的量子反应散射动力学研究+ D反应为2.28 eV，远低于CI。通过观察前向方向周围微分截面中的明显振荡，可以清楚地识别出GP效应。量子动力学理论表明，GP效应是由波函数的一小部分的相变引起的，这与准经典轨迹计算所揭示的现象类似，它对应于一种异常的漫游样抽象路径。