Department of Physics, Texas A&M University, College Station, Texas 77843, USA.
J Chem Phys. 2012 Aug 7;137(5):054202. doi: 10.1063/1.4739315.
Molecular collisions can be studied at very low relative kinetic energies, in the milliKelvin range, by merging codirectional beams with much higher translational energies, extending even to the kiloKelvin range, provided that the beam speeds can be closely matched. This technique provides far more intensity and wider chemical scope than methods that require slowing both collision partners. Previously, at far higher energies, merged beams have been widely used with ions and/or neutrals formed by charge transfer. Here, we assess for neutral, thermal molecular beams the range and resolution of collision energy that now appears attainable, determined chiefly by velocity spreads within the merged beams. Our treatment deals both with velocity distributions familiar for molecular beams formed by effusion or supersonic expansion, and an unorthodox variant produced by a rotating supersonic source capable of scanning the lab beam velocity over a wide range.
分子碰撞可以在非常低的相对动能下进行研究，在毫开尔文范围内，通过合并具有更高平移能的同向光束来实现，甚至可以扩展到千开尔文范围，前提是光束速度可以紧密匹配。这种技术提供的强度和化学范围比需要同时降低两个碰撞伙伴速度的方法广泛得多。以前，在更高的能量下，合并光束已被广泛用于通过电荷转移形成的离子和/或中性。在这里，我们评估了中性、热分子束现在可达到的碰撞能范围和分辨率，主要由合并光束内的速度分布决定。我们的处理方法既适用于通过扩散或超音速膨胀形成的分子束的速度分布，也适用于由旋转超音速源产生的非传统变体，该源能够在很宽的范围内扫描实验室光束速度。
