Positron Impact Electronic Excitation Of N2

We present the results of scattering cross sections for positron impact excitation of electronic states of nitrogen molecule (N2) using the Schwinger multichannel method (SMC). All calculated cross sections took three collision channels into account (X1Σg and degenerate a1Πg states). Present theoretical results for excitation to the a1Πg states failed to reproduce the near-threshold structure observed in the recent and the only available experimental data [Sullivan et al., Phys. Rev. Lett. 87 (2001) 073201-1]. Scattering calculations from the a1Πg states (elastic and superelastic) are also reported. A spurious resonant structure found in the excitation to the a1Πg states was detected in a square integrable basis set calculation designed to reproduce the first Born approximation (FBA). Such spurious structure was removed by taking out the trial configuration state functions in which the positron was weakly coupled to the target. This may be a promising technique to separate unphysical resonances from the physical ones. We also observe that a combination between SMC scattering amplitudes (l≤2) with FBA ones (l≥3) significantly improved the cross sections at higher energies. © 2004 Elsevier B.V. All rights reserved.2211-46975Gilbert, S.J., Sullivan, J.P., Greaves, R., Surko, C.M., (2000) Nucl. Instr. and Meth. B, 171, p. 81Sullivan, J.P., Marler, J.P., Gilbert, S.J., Buckman, S.J., Surko, C.M., (2001) Phys. Rev. Lett., 87, pp. 073201-073211Sullivan, J.P., Gilbert, S.J., Surko, C.M., (2001) Phys. Rev. Lett., 86, p. 1494Surko, C.M., (2001) New Directions in Antimatter Chemistry and Physics, p. 345. , Kluwar Academic PublishersMurphy, T.J., Surko, C.M., (1992) Phys. Rev. A, 46, p. 5695Greaves, R.G., Tinkle, M.D., Surko, C.M., (1994) Phys. Plasmas, 1, p. 1439Germano, J.S.E., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 3976Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1994) Phys. Rev. A, 49, pp. R1527Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1996) Phys. Rev. Lett., 77, p. 1028Da Silva, E.P., Germano, J.S.E., Lino, J.L.S., De Carvalho, C.R.C., Natalense, A.P.P., Lima, M.A.P., (1998) Nucl. Instr. and Meth. B, 143, p. 140De Carvalho, C.R.C., Varella, M.T.D.N., Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (2000) Nucl. Instr. and Meth. B, 171, p. 33Hunt, W.J., Goddard III, W.A., (1974) Chem. Phys. Lett., 24, p. 464Sullivan, J.P., Gilbert, S.J., Buckman, S.J., Surko, C.M., (2001) J. Phys. B, 34, pp. L467Bromley, M.W.J., Mitroy, J., (2003) Phys. Rev. A, 67, p. 062709Rescigno, T.N., (2003), private communicationSzabo, A., Ostlund, N.S., (1989) Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory, , New York: McGraw-Hil

Progress With The Schwinger Multichannel Method In Positron-molecule Scattering

We report calculations for low-energy positron-C2H2 and -N2 scattering obtained through the Schwinger multichannel method (SMC). Integral and differential cross-sections and the annihilation parameter, Zeff, are presented. For nitrogen, evidence of a Ramsauer-Townsend minimum and the possibility of overcorrelation in the scattering configuration space are discussed. Annihilation probability densities (APD) calculated for He and H2 seem to bring indirect support to a model previously proposed to explain why acetylene, unlike nitrogen, presents very high low-energy annihilation rates.17113346Brandt, W., Dupasquier, A., (1983) International School of Physics Enrico Fermi, Positron Solid-State Physics, , (Eds.), Società Italiana di FisicaPuska, M.J., Nieminen, R.M., (1994) Rev. Mod. Phys., 66, p. 841Krause-Rehberg, R., Leipner, H.S., Abgarjan, T., Polity, A., (1998) Appl. Phys. a, 66, p. 599Murphy, T.J., Surko, C.M., (1991) Phys. Rev. Lett., 67, p. 2954Iwata, K., Greaves, R.G., Murphy, T.J., Tinkle, M.D., Surko, C.M., (1995) Phys. Rev. a, 51, p. 473Germano, J.S.E., Lima, M.A.P., (1993) Phys. Rev. a, 47, p. 3976Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1994) Phys. Rev. a, 49, p. 1527Lino, J.L.S., Germano, J.S.E., Da Silva, E.P., Lima, M.A.P., (1998) Phys. Rev. a, 58, p. 3502De Carvalho, C.R.C., Varella, M.T.D.N., Lima, M.A.P., Da Silva, E.P., Germano, J.S.E., (1999) Phys. Rev. Lett., , submitted for publicationIwata, K., Greaves, R.G., Surko, C.M., (1997) Phys. Rev. a, 55, p. 3586Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1996) Phys. Rev. Lett., 77, p. 1028Fraser, P.A., (1968) Adv. At. Mol. Phys., 4, p. 63Van Reeth, P., Humberston, J.W., (1998) J. Phys. B, 31, p. 231Przybyla, D.A., Addo-Asah, W., Kauppila, W.E., Kwan, C.K., Stein, T.S., (1999) Phys. Rev. a, 60, p. 359Sueoka, O., Mori, S., (1989) J. Phys. B, 22, p. 963Danby, G., Tennyson, J., (1991) J. Phys. B, 24, p. 3517Charlton, M., Griffith, T.C., Heyland, G.R., Wright, G.L., (1983) J. Phys. B., 16, p. 323Hoffman, 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., Hamada, A., (1993) J. Phys. Soc. Jpn., 62, p. 2669Coleman, P.G., Griffith, T.C., (1973) J. Phys. B, 6, p. 2155Heyland, G.R., Charlton, M., Griffith, T.C., Wright, G.L., (1982) Can. J. Phys., 60, p. 503Sharma, S.C., McNutt, J.D., (1978) Phys. Rev. a, 18, p. 1426Tao, S.J., (1970) Phys. Rev. a, 2, p. 1669Schneider, B., Collins, L.A., (1984) Phys. Rev. a, 30, p. 95Winstead, C., McKoy, V., (1998) Phys. Rev. a, 57, p. 3589Joachain, C.J., (1975) Quantum Collision Theory, p. 258. , North-Holland, Amsterda

Annihilation Dynamics Of Positrons In Molecular Environments

We present recent results for positron-molecule scattering obtained with the Schwinger multichannel method. Our calculations include integral, differential and momentum transfer cross sections and the annihilation parameter Zeff for C2H2 and C2H4 molecules. We discuss a mechanism for annihilation of positrons in low-energy positron-molecule scattering. We interpret the annihilation process through virtual electronic excitation of the target combined with electronic cloud relaxation and virtual positronium formation. We study the influence of the first electronic state of the target on the cross section and on the annihilation parameter in C+-C2H2 scattering. © 1998 Elsevier Science B.V. All rights reserved.1431-2140148Murphy, T.J., Surko, C.M., (1991) Phys. Rev. Lett., 67, p. 2954Iwata, K., Greaves, R.G., Murphy, T.J., Tinkle, M.D., Surko, C.M., (1995) Phys. Rev. A, 51, p. 473Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1996) Phys. Rev. Lett., 77, p. 1028Germano, J.S.E., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 3976Joachain, C.J., (1975) Quantum Collision Theory, p. 594. , North-Holland, OxfordDa Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1994) Phys. Rev. A, 49, pp. R1527Fraser, P.A., (1968) Adv. Atom. Mol. Phys., 4, p. 63Przybyla, D.A., Addo-Asah, W., Kauppila, W.E., Kwan, C.K., Stein, T.S., (1997) Positron Workshop on Low-Energy Positron and Positronium Physics, p. 26. , NottinghamSueoka, O., Mori, S., (1986) J. Phys. B, 19, p. 4035Herzberg, G., Molecular Spectra and Molecular Structure, p. 611. , Copyright 1966 by Litton Educational PublishingSueoka, O., Mori, S., (1989) J. Phys. B, 22, p. 96