Scattering resonances play a central role in collision processes in physics and chemistry. They help build an intuitive understanding of the collision dynamics due to the spatial localization of the scattering wavefunctions. For resonances that are localized in the reaction region, located at short separation behind the centrifugal barrier, sharp peaks in the reaction rates are the characteristic signature, observed recently with state-of-the-art experiments in low-energy collisions. If, however, the localization occurs outside of the reaction region, mostly the elastic scattering is modified. This may occur due to above-barrier resonances, the quantum analogue of classical orbiting. By probing both elastic and inelastic scattering of metastable helium with deuterium molecules in merged-beam experiments, we differentiate between the nature of quantum resonances—tunnelling resonances versus above-barrier resonances—and corroborate our findings by calculating the corresponding scattering wavefunctions.

散射共振在物理和化学的碰撞过程中起着核心作用。由于散射波函数的空间定位，它们有助于建立对碰撞动力学的直观理解。对于位于反应区域中的共振，位于离心屏障后面的短距离处，反应速率的尖峰是特征特征，最近在低能碰撞的最新实验中观察到。然而，如果定位发生在反应区域之外，则大部分弹性散射都会被修改。这可能是由于上述势垒共振（经典轨道的量子模拟）而发生的。通过在合并束实验中探测亚稳态氦与氘分子的弹性和非弹性散射，