Development of the Cold Collision Electron Spectroscopy

原子和分子目标对极低能电子的散射预计将受到量子效应的强烈支配，涉及量子干涉等现象，并揭示出新的和意想不到的行为。最近，在几百meV以下的极低能量下测量电子分子碰撞总截面的实验技术得到了发展。单色化同步辐射(SR)在原子的近阈值光致电离中产生的单能光电子被用作他们的技术的源。这项技术使得产生非常低能量的电子束成为可能，甚至低于相当于室温的~40 meV的能量。然而，在它们的设置中，电子束的能量宽度取决于单色化SR的光斑大小和带宽，这是激发光子束的光子通量之间的权衡。因此，高亮度的入射光子束是必要的。在本研究中，我们开发了一种高效的冷碰撞实验技术，该技术的关键是利用穿透场来修正“0”能量的光电子，而不是在光电离区施加恒定的电场。在高分辨光子束条件下，阈值峰值是不对称的，表现为高能端上升较快，下降较慢。这种缓慢的脱落对应于从相互作用区直接发射到电子透镜中的高能或“热”电子。在第二级光学系统中，可以通过适当的电势来减小高能尾部。在我们的新装置下，我们用束流衰减法成功地获得了Xe原子的总电子散射截面。

The scattering of very low energy electrons by atomic and molecular targets are expected to be strongly dominated by quantum effects involving phenomena such as quantum interference and revealing new and unexpected behavior. Recently, experimental technique for measuring the total cross section of the electron molecule collisions at very low energy of below a few hundred meV was developed. Mono-energetic photoelectrons produced in the near-threshold photoionization of atoms by monochromatized Synchrotron Radiation (SR) were used as a source in their technique. This technique made it possible to produce very low energy electron beam, even below the energy of〜40 meV, which corresponds to the room temperature. In their setup, however, the energy width of the electron beam depends on the spot size and the band width of the monochromatized SR, which are trade-off between the photon flux of the excitation photon beam. Therefore, highly brilliant incident photon beam was necessary. In the present research, we developed a new experimental technique Cold Collision experiment utilizing the SR with much highly efficiency.The key of the present technique is to use the penetration field to correct only the "0" energy photoelectrons, instead of applying the constant filed across the photoionization region. Under high resolution photon beam conditions, threshold peaks are asymmetric, characterized by a sharp rise and a more slow fall off in the high energy side. The slow fall off corresponds to energetic or 'hot' electrons that are emitted from the interaction region directly into the electron lens. The high energy tail can be reduced by appropriate potentials in the second stage of the optics. We successfully obtained the total electron scattering cross sections of Xe by the beam attenuation method with our new setup.