Low energy electron energy-loss spectroscopy of CF₃X (X=Cl,Br)

We report threshold electron energy-loss spectra for the fluorohalomethanes CFC₃X (X=Cl,Br). Measurements were made at incident electron energies of 30 and 100 eV in energy-loss range of 4-14 eV, and at scattering angles of 4 degrees and 15 degrees. Several new electronic transitions are observed which are ascribable to excitation of low-lying states as well as are intrinsically overlapped in the molecules themselves. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-section measurements, high-energy scattering spectra, and ab initio molecular orbital calculations. The calculated potential curves along the C-X bond show repulsive nature, suggesting that these transitions may lead to dissociation of the C-X bond. The present results are also compared with the previous ones for CF₃H, CF₄, and CF₃I.This work was performed with the support and under the auspices of the CUP, the IAEA’s Co-ordinated Research Program, MEXT, and JAEA. One of the authors C.M. had been also thankful to the Japan Society for Promotion of Science for financial support under Grant No. P04064. One of the authors L.P. also acknowledges partial support by the Academic Frontier Program of MEXT. One of the authors H.C. acknowledges the support from the Korea Research Foundation 2006-311-C00031

A positron trap and beam apparatus for atomic and molecular scattering experiments

An instrument has been designed and constructed to provide new insights into fundamental, low energy positron scattering processes. The design is based on the Surko trap system and produces a pulsed positron beam with an energy resolution of as good as 54 meV. The design and operation of the apparatus is explained, while the first experimental results from this apparatus have been demonstrated in recent publications.The authors would like to acknowledge the Australian Research Council for funding support, through the Centre of Excellence program, as well as the LIEF and Discovery funding programs

Electron And Positron Scattering From 1,1- C2 H2 F2

1,1-difluoroethylene (1,1- C2 H2 F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90° and 120° for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (2 and 9) stretching and the combined C-F (3) stretching and C H2 (11) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B2, B1, and A1 symmetries, respectively. The π* resonance peak at 1.8 eV in C2 H4 is observed shifted to 2.3 eV in 1,1- C2 H2 F2 and to 2.5 eV in C2 F4; a phenomenon attributed to the decreasing CC bond length from C2 H4 to C2 F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV. © 2007 American Institute of Physics.12616(1997) Kyoto Protocol to the United Nations Framework Convention on Climate Change, , http://www.cnn.com/SPECIALS/1997/global.warming/stories/treaty, DecemberMitsui, Y., Ohira, Y., Yonemura, T., Takaichi, T., Sekiya, A., Beppu, T., (2004) J. Electrochem. Soc., 151, p. 297Panajotovic, R., Kitajima, M., Tanaka, H., Jelisavic, M., Lower, J., Campbell, L., Brunger, M.J., Buckman, S.J., (2003) J. Phys. B, 36, p. 1615Szmytkowski, C., Kwitnewski, S., Ptasinska-Denga, E., (2003) Phys. Rev. A, 68, p. 032715Brescansin, L.M., MacHado, L.E., Lee, M.-T., (1998) Phys. Rev. A, 57, p. 3504Winstead, C., McKoy, V., (2002) J. Chem. Phys., 116, p. 1380. , 0021-9606 10.1063/1.1429649Winstead, C., McKoy, V., Bettega, M.H.F., (2005) Phys. Rev. A, 72, p. 042721Coggiola, M.J., Flicker, W.M., Mosher, O.A., Kuppermann, A., (1976) J. Chem. Phys., 65, p. 2655Edgell, W.F., Byrd, W.E., (1949) J. Chem. Phys., 17, p. 740Smith, D.C., Nielsen, J.R., Classen, H.H., (1950) J. Chem. Phys., 16, p. 326Joyner, P., Glockler, G., (1952) J. Chem. Phys., 20, p. 302Roberts, A., Edgell, W.F., (1949) J. Chem. Phys., 17, p. 742. , 0021-9606Roberts, A., Edgell, W.F., (1949) Phys. Rev., 76, p. 178Allan, M., Craig, N.C., McCarty, L.V., (2002) J. Phys. B, 35, p. 523Wahl, R.L., (2002) Principles and Practice of Positron Emission Tomography, , Lippincott, New York/ Williams and Wilkins, BaltimoreSchultz, P.J., Lynn, K.G., (1988) Rev. Mod. Phys., 60, p. 701Mitroy, J., Bromley, M.W.J., Ryzhikh, G.G., (2002) J. Phys. B, 35, p. 81Sueoka, O., Mori, S., Hamada, A., (1994) J. Phys. B, 27, p. 1452Kimura, M., Makochekanwa, C., Sueoka, O., (2004) J. Phys. B, 37, p. 1461Hoffman, K.R., Dababneh, M.S., Hsieh, Y.F., Kauppila, W.E., Pol, V., Smart, J.H., Stein, T.S., (1982) Phys. Rev. A, 25, p. 1393Sueoka, O., Mori, S., (1986) J. Phys. B, 19, p. 4035Sueoka, O., Makochekanwa, C., Kawate, H., (2002) Nucl. Instrum. Methods Phys. Res. B, 192, p. 206Tanaka, H., Ishikawa, T., Masai, T., Sagara, T., Boesten, L., Takekawa, M., Itikawa, Y., Kimura, M., (1998) Phys. Rev. A, 57, p. 1798Srivastava, S.K., Chutjian, A., Trajmar, S., (1975) J. Chem. Phys., 63, p. 2659Takatsuka, K., McKoy, V., (1981) Phys. Rev. A, 24, p. 2473. , 1050-2947 10.1103/PhysRevA.24.2473Takatsuka, K., McKoy, V., (1984) Phys. Rev. A, 30, p. 1734Bettega, M.H.F., Ferreira, L.G., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 1111Bettega, M.H.F., Natalense, A.P.P., Lima, M.A.P., Ferreira, L.G., (2003) J. Phys. B, 36, p. 1263Lopes, A.R., Bettega, M.H.F., (2003) Phys. Rev. A, 67, p. 032711Varellado, T.M.N., Bettega, M.H.F., Lima, M.A.P., Ferreira, L.G., (1999) J. Chem. Phys., 111, p. 6396Rescigno, T.N., McCurdy, C.W., Schneider, B.I., (1989) Appl. Phys. Lett., 63, p. 248Winstead, C., McKoy, V., (1998) Phys. Rev. A, 57, p. 3589Bauschlicher, C.W., (1980) J. Chem. Phys., 72, p. 880(1998) CRC Handbook of Chemistry and Physics, , 79th ed., edited by D. R.Lide (CRC, Boca Raton, FLSueoka, O., Mori, S., (1989) J. Phys. B, 22, p. 963Panajotovic, R., Jelisavcic, M., Kajita, R., Tanaka, T., Kitajima, M., Cho, H., Tanaka, H., Buckman, S.J., (2004) J. Chem. Phys., 121, p. 4559Winstead, C., Sun, Q., McKoy, V., (1992) J. Chem. Phys., 96, p. 4246Kato, H., Makochekanwa, C., Hoshino, M., Kimura, M., Cho, H., Kume, T., Yamamoto, A., Tanaka, H., (2006) Chem. Phys. Lett., 425, p. 1Carlos Jr. J., L., Karl Jr. R., R., Bauer, S.H., (1974) J. Chem. Soc., Faraday Trans. 2, 2, p. 177Chiu, N.S., Burrow, P.D., Jordan, K.D., (1979) Chem. Phys. Lett., 68, p. 121Kimura, M., Sueoka, O., Makochekanwa, C., Kawate, H., Kawada, M., (2001) J. Chem. Phys., 115, p. 744

Absolute elastic differential cross sections for electron scattering by C6 H5 CH3 and C6 H5 CF3 at 1.5-200 eV: A comparative experimental and theoretical study with C6 H6

We present absolute differential cross sections (DCS) for elastic scattering from two benzene derivatives C6 H5 CH3 and C6 H5 CF3. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles 15°-130° and impact energies 1.5-200 eV. DCS results for these two molecules were compared to those of C6 H6 from our previous study. We found that (1) these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5-200 eV, although DCS for C6 H5 CF3 increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and (2) that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV. © 2009 The American Physical Society.F.B. and G.G. were also supported by the Spanish Ministerio de Ciencia e Innovación Project No. FIS0032-00702 and the European Science Foundation EIPAM network and COST Action CM0601.Peer Reviewe

Electron and positron scattering from 1,1-C₂H₂F₂

1,1-difluoroethylene (1,1-C₂H₂F₂) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (ν₂ and ν₉) stretching and the combined C-F (ν₃) stretching and CH₂ (ν₁₁) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B₂, B₁, and A₁ symmetries, respectively. The pi* resonance peak at 1.8 eV in C₂H₄ is observed shifted to 2.3 eV in 1,1-C₂H₂F₂ and to 2.5 eV in C₂F₄; a phenomenon attributed to the decreasing C=C bond length from C₂H₄ to C₂F₄. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV.The work was supported in part by a Grant-in-Aid, the Ministry of Education, Science, Technology, Sport and Culture, Japan, the Japan Society for the Promotion of Science JSPS, and the Japan Atomic Energy Research Institute JAERI. One of the authors C.M. is also grateful to the JSPS for financial support under Grant No. P04064. Another author H.T. acknowledges Dr. T. Ozeki of the JAERI for his encouragement and support during this work. This work was also done under the International Atomic Energy Agency IAEA project for three of the authors C.M., M.H., and H.T.. Two of the authors M.H.F.B. and M.A.P.L. acknowledge support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq. MHFB also acknowledges support from the Paraná state agency Fundação Araucária and from FINEP ( under Project No. CT-Infra 1)

Elastic Differential Cross Sctions for Electron Collisions with Polyatomic Molecules

Experimental data for electron-polyatomic molecule collisions are reviewed in connection with fusion and processing plasmas, as well as with the associated environmental issues. The electron scattering experiments for differential cross section (DCS) measurements for various processes, such as elastic scattering, have been performed across a broad range of energies (1-100 eV), mainly, at Sophia University since 1978, and some done under the collaborations with the Australian National University, Flinders University, and the Chungnam National University. As a benchmark cross section, elastic DCS are essential for the absolute scale conversion of inelastic DCS, as well as for testing computational methods. The need for cross-section data for a wide variety of molecular 2 species is also discussed, because there is an urgent need to develop an international program to provide the scientific and technological communities with authoritative cross sections for electron-molecule interactions. Note that the detailed comparison with other data available is not given here. Ruther, other available data can be found in the references we cite. This course of action was adopted to keep this report to a sensible length, so that only our numerical data is provided here

Electron transfer during the dissociation of CH3F+ produced by resonant photoemission following F 1s excitation

We present experimental evidence for pronounced electron transfer from C to F(+) happening during the breakup of CH(3)F(+) ions in gas phase produced by resonant photoemission following F 1s -> 6a(1)(*) core excitation of CH(3)F. We measured the momentum of the ionic fragments in coincidence with the F KVV Auger electrons that show a Doppler shift reflecting the motion of the F nucleus. The correlation between Doppler shift and ion momentum is opposite for the F(+) and the CH(2)(+) fragments, indicating that CH(2)(+) is produced by electron transfer from C to F(+), after the Auger electron emission from excited moving F. This finding is rationalized by calculations of the potential energy curves of the main states involved in the excitation and decay processes

Electron and positron scattering from 1,1-C2H2F2

1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (nu(2) and nu(9)) stretching and the combined C-F (nu(3)) stretching and CH2 (nu(11)) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B-2, B-1, and A(1) symmetries, respectively. The pi* resonance peak at 1.8 eV in C2H4 is observed shifted to 2.3 eV in 1,1-C2H2F2 and to 2.5 eV in C2F4; a phenomenon attributed to the decreasing C=C bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV. (c) 2007 American Institute of Physics.1261