Photon Factory Activity Report 2014 #32 (2015) B

BL-20A/2014G518

High resolution measurement of total cross section for electron scattering from CO2
Masashi Kitajima*1, Atsushi Kondo1, Keisuke Shigemura1, Takeshi Odagiri2, Masamitsu Hoshino2,
and Hiroshi Tanaka2
1
Department of Chemistry, Tokyo Inst. Tech., Meguro-ku, Tokyo 152-8551, Japan2
Department of Physics, Sophia Univ., Chiyoda-ku, Tokyo 102-8554, Japan

2 Experiment
The experiment has been carried out at the beamline
20A of the Photon Factory, KEK. Present experimentutilizes the penetrating field technique together with thethreshold photoionizaion of atoms by the synchrotron
radiation. 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 are detected by the channel
electron multiplier. The counting rates of the detected
electrons in the presence and absence of target gas areconverted to the total cross section for electron scattering
according to the attenuation law.
3 Results and Discussion
Total cross sections for electron scattering from CO2 atelectron energies down to about 150 meV are shown inFig. 1. A reasonable agreement was obtained between
present cross-section values and the previous results
down to around 1 eV. In the present measurement, theoscillatory structure at the 2u shape resonance region
was successfully observed on the total cross-section curve,
which was turned out to be very weak. At very low
energy region below 200 meV, the present results agree
well with the results obtained by Field et al. [2], whichshows slightly larger cross-section values from others.
50
Present work
Ferch et al., J. Phys. B 14 L97 (1981)
Hoffman et al., Phys. Rev. A 25 1393 (1982)
Buckman et al., J. Phys. B 20 5175 (1987)
Szmytkowski et al., J. Phys. B 20 5817 (1987)
Kimura et al., J. Chem. Phys. 107 6616 (1997)
Field et al., Phys. Rev. A 64 022708 (2001)

4030-20

2

Cross sections (10 m )1 Introduction
The scattering of low-energy electrons by atoms andmolecules has been the subject of extensive experimentaland theoretical investigations. The cross-section data
concerning electron-atom or -molecule scattering are ofgreat importance in understanding fundamental physics ofthe electron collisions and applications in many fields.
Electron scattering from CO2 is one of the basic processes
involving the molecule and studied both theoretically andexperimentally since the 1920s. A large number of papers
have been published to report data for the total crosssections and differential cross sections for electron
scattering from CO2. Several reports for cross section
measurements in the energy region down to 1 eV areconsistent with each other and recommended crosssection data were presented [1]. Low-energy electron
scattering from CO2 represents a particularly interesting
system, which is dominated by the 2u shape resonance ataround collision energy of 4 eV and a dramatic rise in the
total cross section below 1 eV, which has been attributed
to the effect from the virtual state [2]. In addition to thelarge enhancement of the cross section, an oscillatory
structure in the transmitted electron current has beenobserved at the 2u shape resonance region [3]. Theoscillatory structure at the shape resonance region wasenhanced in the vibrational excitation cross sections,however, the position and its spacing differs withdifferent excitation channels. The oscillations of the crosssections are due to the rapid variation of the resonancewidth with the change of the nuclear coordinate of theparent molecule. Although the oscillatory structures in thedifferential cross sections have been obtained in theseveral experiments, the structures have not beenobtained in the total cross section measurement.
Recently, we have developed a new method for
producing an electron beam at very high resolution
employing the synchrotron radiation (SR), i.e., thethreshold photoelectron source [4]. In the present project,
we have measured total cross sections of electronscattering from CO2 below 10 eV.

2010CO20.1

110Electron Energy (eV)Fig. 1 Total cross section of electron scattering from CO2.

References[1] Y. Itikawa, J. Phys. Chem. Ref. Data 31, 749 (2002)[2] D. Field et al., Phys. Rev. A 64, 022708 (2001)[3] L. Sanche and G. J. Schulz, J. Chem. Phys. 58 479(1973)[4] M. Kurokawa et al., Phys. Rev. A 82, 062707 (2010)* mkitajim@chem.titech.ac.jp