Feshbach-resonance-mediated positron annihilation in small molecules
Feshbach-resonance-mediated positron annihilation in small molecules
复制标题
小分子中费什巴赫共振介导的正电子湮灭
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
C. Surko
中科院分区：
文献类型：
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作者：
J. Young;C. Surko
大的正电子湮没截面已被观察到各种分子在各种能量低于正电子素形成的阈值。这些大值是由于振动Feshbach共振VFR，其中正电子附着在分子上，同时激发振动。这导致湮灭率远远大于简单碰撞的预期。湮没率对入射正电子能量的依赖关系可以用来推导正电子与分子的结合能。这里提出的是一个全面的研究共振湮灭在小分子，例如，具有一个或两个碳原子的碳氢化合物。在某些情况下，只有基本振动是重要的，理论正确地预测了湮灭率作为入射正电子能量的函数。在其他情况下，组合和泛音振动显示支持Feshbach共振。在这些情况下，正电子-分子耦合强度可以确定这些组合模式的子集，理论预测与测量一致。最后，还有一些物种不表现出VFR，如二氧化碳。这被解释为正电子与这些靶的结合非常弱或根本不结合的证据。这些分子中有几种表现出各种目前无法解释的行为。这里提出的正电子湮没分子的更全面的理论的结果的影响进行了讨论。
Large positron annihilation cross sections have been observed for a variety of molecules at various energies below the threshold for positronium formation. These large values are due to vibrational Feshbach resonances VFRs , in which the positron attaches to the molecule while exciting a vibration. This leads to rates of annihilation far greater than those expected for a simple collision. The dependence of the annihilation rate on incident positron energy can be used to deduce positron-molecule binding energies. Presented here is a comprehensive study of resonant annihilation in small molecules e.g., hydrocarbons with one or two carbon atoms . In some cases, only fundamental vibrations are important, and theory correctly predicts the annihilation rates as a function of incident positron energy. In other cases, combination and overtone vibrations are shown to support Feshbach resonances. In the subset of these cases where the positron-molecule coupling strengths can be determined for these combination modes, theoretical predictions are in agreement with the measurements. Finally, there are species that do not exhibit VFRs, such as carbon dioxide. This is interpreted as evidence that positrons bind very weakly or not at all to these targets. Several of these molecules exhibit a variety of behaviors that are presently unexplained. The implications of the results presented here for more comprehensive theories of positron annihilation on molecules are discussed.