Photon Factory Activity Report 2016 #34 (2017)

BL-20A/2016G521

Ultra-low-energy total cross sections for electron scattering from N2O
Masashi Kitajima1,*, Atsushi Sayama1, Naomasa Kobayashi1, Yuma Mori1, Takuma Okumura1,Hirofumi Akasaka1, Kouichi Hosaka1, Takeshi Odagiri2, Masamitsu Hoshino2, and Hiroshi Tanaka2
1
Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan2
Department of Material and Life Sciences, Sophia University, Chiyoda-ku, Tokyo 102-8554, Japan
1 Introduction
Accurate absolute cross section data for electronscattering from atoms and molecules provide important
information not only for the fundamental physics ofelectron collisions but also for many fields such as
electron-driven processes in the Earth and planetaryphenomena, gaseous discharges, radiation chemistry andplasmas physics. Consequences of several interesting
scattering phenomena such as Ramseur - Townsend effect,
shape resonances, vibrational Feshbach resonances, andthreshold structure due to a virtual state, appear in thescattering cross section curves especially at very-low
collision energies, where the de Broglie wavelength of anelectron become much longer than the typical size oftarget particles. The low energy behaviors of the electron
scattering cross sections are also related to the scattering
length which gives zero-energy scattering cross section.
Present group have developed a unique experimental
technique in order to measure absolute total cross sections
for electron scattering from atoms and molecules, whichmakes use of photoelectrons produced by thephotoionization of atoms using Synchrotron Radiation(SR) instead of using the conventional hot-filamentelectron sources [1-4]. The technique enables one tomeasure total electron scattering cross sections down tovery-low energies with extremely high energy resolution
in the single collision condition.
In the present project, total cross sections for electron
scattering from nitrous oxide were measured in a wide
energy range including the very-low energy region below
100 meV, where no experimental values had beenreported.
2 Experiment
The experiment has been carried out at the beamline
20A of the Photon Factory, KEK. Present experimentemploys the threshold photoelectron source utilizing theSR which utilizes the penetrating field technique together
with the threshold photoionization of noble gas atoms by
the SR. The threshold photoelectrons produced by thethreshold photoionization of Ar are extracted by a weakelectrostatic field formed by the penetrating fieldtechnique and formed into a beam. The intensity of theelectron beam passing through the collision cell without
any collision with the target was detected by the channel
electron multiplier. The counting rates of the detected
electrons were measured as a function of the number
density of the target gas filled in the gas cell in order toobtain the total cross section for electron scattering

according to the attenuation law. The continuous injection
operation of the PF ring is one of the key feature for thereliable absolute value measurements of the total crosssections.
3 Results and Discussion
Total cross sections for electron scattering from N2O atelectron energies from 20 eV down to about 20 meV
obtained in the present work are shown in Fig. 1 together
with previously reported experimental cross sections.
Present results shows strong increase toward the zeroenergy limit. The total cross section curve shows intense
broad structure at around 2.5 eV due to the shaperesonance which shows a reasonable agreement with theprevious results. Present results showed thatrecommended values reported in 2003 [5], which havebeen obtained from compilation of several previous
experimental results, have underestimated the crosssection values at energies below 1 eV. Here we mark afininding that the cross section curve shows a cusp likefeature just at the threshold of the vibrational excitationenergy which is very interseting.

Fig. 1 Total cross sections for electron scatteringfrom N2O.
References[1] M. Kurokawa et al., Phys. Rev. A 82, 062707 (2010).
[2] M. Kurokawa et al., Phys. Rev. A 84, 062717 (2011).
[3] K. Shigemura et al., Phys. Rev. A 89, 022709 (2014).
[4] M. Kitajima et al., Eur. Phys. J. D 71, 139 (2017)[5] A. Zecca et al., Int. J. Mass Spectrom., 223-224 205(2003).
* mkitajim@chem.titech.ac.jp