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-ƒ¿ 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 (ƒÁ, 2ƒÁ) method, to investigate the multiply excited
molecules. In (ƒÁ, 2ƒÁ) 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 (ƒÁ, 2ƒÁ) 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 (ƒÁ,ƒÁ) experiment
(detect only one fluorescence photon from neutral fragments produced from multiply excited molecules), and (c) is the result of (ƒÁ, 2ƒÁ) 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, (ƒÁ, 2ƒÁ) 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, (ƒÁ, 2ƒÁ) 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