Mode coupling and multiquantum vibrational excitations in Feshbach-resonant positron annihilation in molecules
Mode coupling and multiquantum vibrational excitations in Feshbach-resonant positron annihilation in molecules
复制标题
分子中费什巴赫共振正电子湮灭的模式耦合和多量子振动激发
DOI：
10.1103/physreva.96.062709
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发表时间：
2017
影响因子：
2.9
通讯作者：
Surko, C. M.
中科院分区：
文献类型：
--
作者：
Gribakin, G. F.;Stanton, J. F.;Danielson, J. R.;Natisin, M. R.;Surko, C. M.
多原子分子中低能正电子湮灭的主要机制是通过振动Feshbach共振（VFR）中的正电子捕获。本文从理论上研究了振动哈密顿量中的非谐项对正电子湮没率的影响。这种相互作用使正电子捕获VFR与多量子振动激发，导致增强湮灭。模式耦合也可以导致VFR的更快的去布居，从而减少它们对湮灭率的贡献。为了分析这个复杂的图片，我们使用耦合簇方法计算的非谐振动光谱和偶极跃迁振幅氯仿，氯仿，1，1-二氯乙烯，甲醇，并使用这些数据来计算这些分子的正电子共振湮灭率。理论预测相比，作为入射正电子能量的函数测得的湮灭率。结果表明，模式耦合在增强和抑制VFR的重要性。也有实验证据的直接激发多模目视飞行规则。他们的贡献进行了分析，使用统计方法，展望更准确地处理这一现象。
The dominant mechanism of low-energy positron annihilation in polyatomic molecules is through positron capture in vibrational Feshbach resonances (VFR). In this paper, we investigate theoretically the effect of anharmonic terms in the vibrational Hamiltonian on positron annihilation rates. Such interactions enable positron capture in VFRs associated with multiquantum vibrational excitations, leading to enhanced annihilation. Mode coupling can also lead to faster depopulation of VFRs, thereby reducing their contribution to the annihilation rates. To analyze this complex picture, we use coupled-cluster methods to calculate the anharmonic vibrational spectra and dipole transition amplitudes for chloroform, chloroform-, 1,1-dichloroethylene, and methanol, and use these data to compute positron resonant annihilation rates for these molecules. Theoretical predictions are compared with the annihilation rates measured as a function of incident positron energy. The results demonstrate the importance of mode coupling in both enhancement and suppression of the VFR. There is also experimental evidence for the direct excitation of multimode VFR. Their contribution is analyzed using a statistical approach, with an outlook towards more accurate treatment of this phenomenon.