Embedded Files
Electron that is an important particle dominating the chemical bonds and reactions
Recently, it is possible to explore and study interactions or chemical reactions between materials in the natural world and material world surrounding us from the viewpoints of the atomic and molecular levels. In general, in order to investigate the internal states of atoms and molecules such as electronic states, vibrational or rotational states, it is one of the effective methods to observe the kinetic energy distributions, momentum distributions and angular distributions of the scattered/emitted electrons and ions generated by the irradiation of electrons, photos, ions, or excited atoms.
For example, electron microscopy has recently attracted as one of the most cutting-edge technologies that is used not only in the field of atomic physics, but also in related chemistry and biology. After J. J. Thomson has discovered the mass-charge ratio of an electron as the particle in his Cathode-ray tube experiments, de Broglie proposed that the electron behaves as a matter wave in quantum theory.
According to de Broglie's formula in which the wavelength in the wave behavior of an electron is inversely proportional to the electron's momentum, and its coefficient is Planck's constant, an electron accelerated by a voltage of about 150 V has its de Broglie wavelength is 1Å. This is about the same as the size of an atom or molecule.
In general, when the wavelength of the incident wave and the size of the target objects are comparable, the incident wave interacts with the target and the wave is distorted most efficiently. This corresponds to the “scattering”. Since the electrons also behave as the wave in the microscopic world as described above, by generating and controlling them in the laboratory, we can observe the responses from atoms and molecules (nano-world) that cannot be seen with ordinary optical microscopes. Furthermore, since de Broglie's formula is inversely proportional to the momentum of electrons, the wavelength can be adjusted by the external accelerating voltage, making it possible to observe atomic and molecular levels today such as electron microscopes.
Electrons also play the role of like a “glue” that binds atomic nuclei positively charged to form molecules, and the existence of light electrons, which are point charges with no size, is important in chemical reactions and in the composition of matter. Without electrons, molecular bonds and chemical reactions do not occur, so they never appear on the front stage, but it is no exaggeration to say that electrons are one of the most important hidden particles in the microscopic world.
Therefore, in our laboratory, through methods of a low-energy electron spectroscopy and a photoelectron spectroscopy, widely-used gaseous atoms and molecules, especially plasma process molecules, nuclear fusion-related molecules, environment-related molecules, biological constituent molecules. Recently, focusing on the target including the solids and liquids, we are conducting experimental research on atomic and molecular excitation processes. We are actively joint research with universities as well as research institutes in foreign countries such as Tokyo Institute of Technology, High Energy Accelerator Research Organization Photon Factory, Japan Atomic Energy Agency, National Institute for Fusion Science in Japan, Universidade NOVA de Lisboa in Portugal and CSIC in Spain.
Collision experiment between low-energy electrons and atoms/molecules at Sophia University
I will introduce our main subjects below.
One of our main research subjects is an electron energy loss spectroscopy. This is one of the most famous experimental techniques to observe the excitation processes of atoms and molecules. The electron energy loss process is expressed as follows.
e- (E0) + A → e- (E0 - ΔE) + A*
Electron accelerated by an external voltage E0 (called “incident energy”) collides with a target A, and the number of scattered electrons is detected as a function of the energy loss ΔE of the scattered electrons.
Here, the process of ΔE = 0 is called "elastic scattering", that is the scattering process in which no incident electron energy is given to the target. This elastic scattering occurs at all incident energies E0 and is the most dominant process in the low-energy region. On the other hand, the process of ΔE ≠ 0 is called “inelastic scattering'', in which the target is excited using a part of kinetic energy of the incident electrons, and the incident electrons lose those kinetic energy (called “electron energy loss”).
When the target is a gas-phase molecule, the value of ΔE depends on the final state of the molecules. When ΔE ~100meV, for example, vibrational excitations will occur that means the molecules start to vibrate by electron impacts. Furthermore, electronic excitation or ionization, sometimes target dissociation will occur above ΔE~ eV order. Therefore, high-resolution electron and photon-beams are required for detailed probing of various scattering processes and molecular final states. In addition, by measuring an angular distribution of scattered electrons in our laboratory, we can also obtain the "differential cross section", which is the most important physical quantity in electron collision phenomena.
In addition, the cross section data sets for these various scattering processes in electron collisions with atoms and molecules are also important as input data for plasma processes, nuclear fusion plasmas, and atmospheric environment simulations. In order to understand complex natural phenomena in such application fields, accurate "fundamental dataset" for more accurate computer simulations (modeling) related to plasma are strongly required. However, the target molecule species, energy ranges corresponding the plasma temperature, and collision processes in these fundamental data are unexpectedly insufficient. In order to model more realistic natural phenomena, research on fundamental processes such as electron collision experiments is quite important subjects.
Angle-resolved electron energy loss spectroscopy of gas-phase atoms and molecules (quantitative measurement of elastic scattering, vibrational excitation, and electronic excitation cross sections)
Electron energy loss spectroscopy experiments on refractory liquid molecules and solid surfaces
Ion detection experiment by electron collision at Sophia University
1. Mass spectrometry experiments by crossed-beam method (quantitative measurement of ionization, dissociation, and dissociative electron attachment cross sections)
Photoelectron spectroscopy of atoms and molecules using synchrotron radiation (High Energy Accelerator Research Organization Photon Factory)
Vacuum ultraviolet photoelectron spectroscopy of heated gas-phase molecules (vibrationally excited molecules)
Vacuum ultraviolet and soft X-ray photoelectron spectroscopy and absorption experiments of soft volatile liquid molecules
If you are interested in our laboratory or our research subjects, please contact us by e-mail.
We welcome you to visit our laboratory at any time.
E-mail: masami-h@sophia.ac.jp
Page updated
Google Sites
Report abuse