Research of Kouchi-Kitajima Laboratory

"New Research by New Method"

Our research interests are

(1) Quantum Dynamics in the multiply excited molecules, (2) Electron-ion coincident measurements, and (3) Cold electron Collisons.

For these purposes, we develop the new experiment method and apparatuses, and do high-level researches by means of them.


Multiply excited state of in electron interaction with molecules as studied by Electron-Energy-Loss Spectroscopy tagged with fluorescence photons

The dynamics of multiply excited molecules(one of the superexcited states molecules) are very interesting subject of current molecular science, because of the breakdown of the independent electron model (i.e. mean-field approximation) and the Born-Oppenheimer approximation. We have been investigated the dynamics of them in the electron-molecules collisions. As well known, the electron-energy-loss spectroscopy(EELS) is a useful means to investigate excited states of atoms and molecules. However, it is difficult to apply this method to investigating the multiply excited molecules, since electron-energy-loss spectra is dominated by large contributions from direct ionization in the range of multiply excited molecules. For this reason, the structures of multiply excited molecules in spectra are embedded by ionization, thus we cannot observe them by usual EELS. Therefore, the elimination of the contributions from ionization is the key point to investigate the multiply excited molecules experimentally.

To overcome this difficulty, we heve estabilished a original method named "Coincident Electron-Energy-Loss Spectroscopy(CoEELS)". In this method, electron-energy-loss spectra tagged with the vacuum ultraviolet(VUV) fluorescence emitted by neutral fragments produced from multiply excited molecules are measured by means of electron-photon coincidence technique. By use of this method, is obtained. By normalize the coincidence count-rate measured at each electron-energy-loss, we can obtain the electron-energy-loss spectra which is free from ionization, i.e. informations of multiply excited molecules experimentally.

Recently, we developed a imaging type CoEELS aparatus, using PSD(Position Sensitive Detector) as scattered-electron detector. For the expansion of the method described above, the same spectra can be obtained more rapidly than above one using EM(Electron Multiplier) as scattered-electron detector.

For more details of this research, please read following papers.

...etc

The CoEELS apparatus (Left), and the result of this method in case of molecular hydrogen (Right)
Right figure is (a) the ordinary and (b) tagged with Lyman- electron-energy-loss spectra of molecular hydrogen. As can be seen from (b),
the peaks around at 26 eV and 34 eV which were not seen in (a), and were observed for the first time by our original method.

Key word ; Electron-molecule collisions, Multiply excited states molecules, Breakdown of the Born-Oppenheimer & the mean-field approximation,
Coincidence technique,
Electron-Energy-Loss Spectroscopy tagged with fluorescence photon,
2D-Coincident Electron-Energy-Loss Spectroscopy


Multiply excited state of molecules in photon interaction with molecules as probed by emissive neutral-dissociation

We also investigate the dynamics of multiply excited molecules in photon-molecule processes, as well as in electron-molecule collisions. However, we have the same difficulty as electron one in case of photon-molecule interaction, i.e. large contributions from ionization in the range of multiply excited molecules in spectra.

To overcome this problem,
recently we have established a new method named (, 2)
method, to investigate the multiply excited molecules.
In (, 2) method, two fluorescence photons from neutral fragments produced from multiply excited molecules are detected by photon-photon coincidence technique. The advantage of this method is that we are able to measure the cross sections free from ionization over an entire range of incident photon energy in photoexcitation of diatomic molecules, and thus the features of multiply excited molecules become noticeable in such a cross section curve.

We have applied this method to some diatomic molecules(H2, N2, O2, NO), and have obtained interesting results about the dynamics of multiply excited molecules for the first time.

The apparatus for (, 2) experiment (Left), and the result of this method in case of molecular nitrogen (Right).
Right figure is from Murata et. al. (J. Phys. B: At. Mol. Opt. Phys., 39 (2006), 1285-1297). (b) is the result of (,) experiment (detect only one
fluorescence photon from neutral fragments produced from multiply excited molecules), and (c) is the result of (, 2) experiment.
Attentions are paid to peak around at 45eV, because the peak is above the double izonization potential (43eV).
It is interesting that highly excited state N2 makes a contribution comparable to those below the double izonization potential.
As evident from this figure, (, 2) method is powerful tool for investigating the dynamics of multiply excited states of
molecules in high energy-range in photon-molecule interaction.

For more details of this research, please read following papers.

Key word ; Photon-molecule interaction, (, 2) method


Development of troidal analyzer for electron-ion coincident measurements

Key word ; troidal analyzer, electron-ion coincident


Cold electron collisions

We investigate the very low energy-electron(~meV)-molecules collision processes. As the energy of elctrons are lower, e.g. far below the energy of room temperature, the de Broglie wavelength of molecules are longer than themselves, and quantal effects are expected to be more noticeable in collision processes. We called these processes as "Cold Collisions".

This project is also newly started and we are now constructing the apparatuses for this experiment eagerly !

The apparatus of Cold Collision experiment (Left ; Chamber, Right ; Electrostatic lenses to generate the low-energy electron beam)

Key word ; Cold electron collisions