Feshbach-resonance-mediated annihilation in positron interactions with large molecules
Feshbach-resonance-mediated annihilation in positron interactions with large molecules
复制标题
正电子与大分子相互作用中费什巴赫共振介导的湮灭
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
正电子对分子湮灭的测量已经确定，正电子通过振动Feshbach共振VFR附着在各种分子上。这些共振，反过来，导致大大增强的正电子湮灭率超出了简单碰撞的预期。最近的一篇论文J. A. Young和C. M. Surko，Phys. Rev. Lett. 99，133201 2007描述了大分子中正电子湮灭的实验研究和分析。这里介绍的是对这些结果以及数据和分析的更完整的描述。正电子分子结合能数据，提出了25个分子，包括相对较深的绑定物种1-氯己烷，苯，和萘。当一个相对较弱的依赖性共振湮没率对入射正电子能量和结合能被删除时，所得到的碳氢化合物的速率被证明服从一个普遍的缩放作为振动自由度的函数。先前测量的湮没率烷烃使用热正电子在300 K的示出与测量在更高的能量在定量上一致。结果部分氟化烃，提供证据表明，在这些分子中观察到的共振湮灭的不寻常的抑制发生通过振动退激过程。讨论了分子温度和非弹性逃逸通道在VFR介导的正电子湮没中的作用。这些结果的湮没过程的理论的影响进行了讨论。
Measurements of positron-on-molecule annihilation have established that positrons attach to a variety of molecules via vibrational Feshbach resonances VFRs. These resonances, in turn, result in greatly enhanced positron annihilation rates beyond those expected in simple collisions. A recent paper J. A. Young and C. M. Surko, Phys. Rev. Lett. 99, 133201 2007 described experimental studies and analysis of positron annihilation in large molecules. Presented here is a more complete description of those results as well as data and analysis. Positron-molecule binding energy data are presented for twenty-five molecules, including the relatively deeply bound species 1-chlorohexane, benzene, and naphthelene. When a relatively weak dependence of resonant annihilation rate on incident positron energy and binding energy is removed, the resulting rates for hydrocarbons are shown to obey a universal scaling as a function of the number of vibrational degrees of freedom. Previously measured annihilation rates for alkanes using thermal positrons at 300 K are shown to be in quantitative agreement with measurements at higher energies. Results are presented for partially fluorinated hydrocarbons, providing evidence that the unusual suppression of resonant annihilation observed in these molecules occurs via a vibrational deexcitation process. The role of molecular temperature and inelastic escape channels in VFR-mediated positron annihilation in molecules is discussed. The implications of these results for theories of the annihilation process are also discussed.