Investigation of quantum states and scattering dynamics of polyatomic molecules by electron and positron impacts

由于电荷的不同，电子(e^-)和正电子(e^)在与原子和分子碰撞时会提供完全不同的相互作用方案和动力学机制。我们研究了(e^-)和e~+碰撞对CO_2和OCS分子的振动激发，因为这两个分子都是线性分子，但OCS分子有弱偶极矩，而CO_2没有偶极矩。我们首次观察到CO_2的e^和e^散射的振动激发对振动模的强烈依赖关系，对于对称伸缩(100)模，e^散射的振动激发截面比e^散射的振动激发截面大2-3个数量级，而非对称伸缩(001)模和弯曲(010)模的振动激发截面非常相似。我们的实验结果与理论结果定性一致。弱四极相互作用和长程强偶极相互作用与耦合矩阵元的结合是造成这一现象的原因。此外，还观察到了大量类共振态结构的存在。

Due to the difference in charge, electrons (e^-) and positrons (e^+) are expected to provide quite different interaction scheme and dynamical mechanisms upon collisions with atoms and molecules. We have investigated vibrational excitation in CO_2 and OCS molecules by (e^-) and e^+ impacts, because both molecules are linear molecules, but OCS molecule has a weak dipole moment while CO_2 has no dipole. We have observed a strong vibrational mode-dependence for vibrational excitation in e^+ and e^- scattering from CO_2 for the first time ; for the symmetric stretching (100) mode, vibrational excitation cross section by e^- scattering is larger by two-three orders of magnitude than that by e^+ scattering, while the cross sections for asymmetric stretching (001) and bending (010) modes are rather similar. Our experimental results are qualitatively consistent to theoretical findings. The weak quadrupole interaction and long-range strong dipole interaction in a combination with the coupling matrix element are responsible to the cause. In addition, the presence of the resonance-like structures was abundantly observed.