Low-energy Positron Scattering By Co2

In this work we present results of integral (ICS) and differential (DCS) cross sections for positron- CO2 scattering at low incident energies. Our ICS shows a significant improvement toward the experimental data, especially below 2 eV, and all the way up to the positronium formation threshold (7.8 eV), in comparison to our previous calculations. Our calculated DCSs show a better resemblance in shape with the quasielastic experimental points of the Detroit group, but the agreement is still not fully satisfactory, indicating a need for further theoretical and experimental investigation. © 2008 The American Physical Society.775Wahl, R.L., (2002) Principles and Practice of Positron Emission Tomography, , Lippincott, Williams and Wilkins, PhiladelphiaGuessoum, N., Ramaty, R., Lengenfeltter, R.E., (1991) Astrophys. J., 378, p. 170. , ASJOAB 0004-637X 10.1086/170417Surko, C.M., Gribakin, G.F., Buckman, S.J., (2005) J. Phys. B, 38, p. 57. , JPAPEH 0953-4075 10.1088/0953-4075/38/6/R01Germano, J.S.E., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 3976. , PLRAAN 1050-2947 10.1103/PhysRevA.47.3976Da Silva, E.P., Germano, J.S.E., Lima, M.A.P., (1994) Phys. Rev. A, 49, p. 1527. , PLRAAN 1050-2947 10.1103/PhysRevA.49.R1527Arretche, F., Da Costa, R.F., D'A. Sanchez, S., Hisi, A.N.S., De Oliveira, E.M., Do Varella N, M.T., Lima, M.A.P., (2006) Nucl. Instrum. Methods Phys. Res. B, 247, p. 13. , NIMBEU 0168-583X 10.1016/j.nimb.2006.01.032De Carvalho, C.R.C., Do Varella N, M.T., Lima, M.A.P., Da Silva, E.P., Germano, J.S.E., (2000) Nucl. Instrum. Methods Phys. Res. B, 171, p. 33. , NIMBEU 0168-583X 10.1016/S0168-583X(00)00036-7D'A. Sanchez, S., Arretche, F., Do Varella N, M.T., Lima, M.A.P., (2004) Phys. Scr., 110, p. 276. , PHSTBO 0031-8949 10.1238/Physica.Topical.110a00276Hoffman, 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. 1393. , PLRAAN 1050-2947 10.1103/PhysRevA.25.1393Przybyla, D.A., Addo-Asah, W., Kaupilla, W.E., Kwan, C.K., Stein, T.S., (1999) Phys. Rev. A, 60, p. 359. , PLRAAN 1050-2947 10.1103/PhysRevA.60.359Bettega, M.H.F., Winstead, C., McKoy, V., (2006) Phys. Rev. A, 74, p. 022711. , PLRAAN 1050-2947 10.1103/PhysRevA.74.022711Rescigno, T.N., Byrum, D.A., Isaacs, W.A., McCurdy, C.W., (1999) Phys. Rev. A, 60, p. 2186. , PLRAAN 1050-2947 10.1103/PhysRevA.60.2186Winstead, C., McKoy, V., (1998) Phys. Rev. A, 57, p. 3589. , PLRAAN 1050-2947 10.1103/PhysRevA.57.3589Chaudhuri, P., Do Varella N, M.T., De Carvalho, C.R.C., Lima, M.A.P., (2004) Phys. Rev. A, 69, p. 042703. , PLRAAN 1050-2947 10.1103/PhysRevA.69.042703Lee, C.H., Winstead, C., McKoy, V., (1999) J. Chem. Phys., 111, p. 5056. , JCPSA6 0021-9606 10.1063/1.479761Kroin, T., Michelin, S.E., Mazon, K.T., Almeida, D.P., Lee, M.T., (1999) J. Mol. Struct.: THEOCHEM, 464, p. 49. , THEODJ 0166-1280 10.1016/S0166-1280(98)00534-XGianturco, F.A., Paioletti, P., (1997) Phys. Rev. A, 55, p. 3491. , PLRAAN 1050-2947 10.1103/PhysRevA.55.3491(1997) CRC Handbook of Chemistry and Physics, , 78th ed., edited by David R. Lide (CRC, Boca RatonSueoka, O., Hamada, A., (1993) J. Phys. Soc. Jpn., 62, p. 2669. , JUPSAU 0031-9015 10.1143/JPSJ.62.2669Zecca, A., Perazzolli, C., Moser, N., Sanyal, D., Chakrabarti, M., Brunger, M.J., (2006) Phys. Rev. A, 74, p. 012707. , PLRAAN 1050-2947 10.1103/PhysRevA.74.012707Morrison, M.A., (1982) Phys. Rev. A, 25, p. 1445. , PLRAAN 1050-2947 10.1103/PhysRevA.25.144

Cross Sections For Rotational Excitation Of Ch4 By 320-ev Electrons

We report calculated differential, integral, and momentum-transfer cross sections for rotational excitation of CH4 by electron impact in the 320-eV energy range. These cross sections were derived from fixed-nuclei scattering amplitudes obtained using the Schwinger multichannel method. Our results represent the first rotational excitation cross sections obtained for a polyatomic molecule using entirely ab initio procedures. The cross sections agree well with those of earlier model-potential calculations. A comparison of these calculated cross sections with available experimental data is in general encouraging, but some discrepancies remain. © 1989 The American Physical Society.40105577558

Polarization Effects On Electronic Excitation Of Molecules By Low-energy Electron Impact: Study On E- -furan Scattering

The Schwinger multichannel method is applied to study the influence of polarization effects on the electronic excitation of the furan molecule by low-energy electron impact. We discuss the importance of inclusion of these effects through the comparison of theoretical results for the electronic excitation of the B3 2 state of furan obtained with and without the proper treatment of the polarization of the target. The electron-furan scattering presents two prominent shape resonances in the A2 2 and B2 1 symmetries at around the electronic excitation threshold of the B3 2 state (3.7 eV). At this low-energy, the inclusion of polarization effects in the calculation moves to lower energies the resonances positions obtained either in the close-coupling or in the static-exchange level of approximation. This phenomenon strongly influences the electronic excitation process. The present results show that a simple close-coupling calculation cannot be applied for molecular systems with low-energy electronic excitation thresholds around misplaced resonances. © 2008 The American Physical Society.771Boudaïffa, B., Cloutier, P., Hunting, D., Huels, M.A., Sanche, L., (2000) Science, 287, p. 1658. , SCIEAS 0036-8075 10.1126/science.287.5458.1658Sanche, L., (2005) Eur. Phys. J. D, 35, p. 367. , EPJDF6 1434-6060 10.1140/epjd/e2005-00206-6Martin, F., Burrow, P.D., Cai, Z., Cloutier, P., Hunting, D., Sanche, L., (2004) Phys. Rev. Lett., 93, p. 068101. , PRLTAO 0031-9007 10.1103/PhysRevLett.93.068101Zecca, A., Perazzolli, C., Brunger, M.J., (2005) J. Phys. B, 38, p. 2079. , 0022-3700Mozejko, P., Sanche, L., (2005) Radiat. Phys. Chem., 73, p. 77. , RPCHDM 0969-806X 10.1016/j.radphyschem.2004.10.001König, C., Kopyra, J., Bald, I., Illenberger, E., (2006) Phys. Rev. Lett., 97, p. 018105. , PRLTAO 0031-9007 10.1103/PhysRevLett.97.018105Winstead, C., McKoy, V., (2006) J. Chem. Phys., 125, p. 244302. , JCPSA6 0021-9606 10.1063/1.2424456Winstead, C., McKoy, V., (2006) J. Chem. Phys., 125, p. 074302. , JCPSA6 0021-9606 10.1063/1.2263824Bouchiha, D., Gorfinkiel, J.D., Caron, L.G., Sanche, L., (2006) J. Phys. B, 39, p. 975. , 0022-3700Trevisan, C.S., Orel, A.E., Rescigno, T.N., (2006) J. Phys. B, 39, p. 255. , 0022-3700Colyer, C.J., Vizcaino, V., Sullivan, J.P., Brunger, M.J., Buckman, S.J., (2007) New J. Phys., 9, p. 41. , NJOPFM 1367-2630 10.1088/1367-2630/9/2/041Bettega, M.H.F., Lima, M.A.P., (2007) J. Chem. Phys., 126, p. 194317. , JCPSA6 0021-9606 10.1063/1.2739514Fleig, T., Knecht, S., Hättig, C., (2007) J. Phys. Chem. A, 111, p. 5482. , 1089-5639Modelli, A., Burrow, P.W., (2004) J. Phys. Chem. A, 108, p. 5721. , JPCAFH 1089-5639 10.1021/jp048759aSulzer, P., Ptasinska, S., Zappa, F., Mielewska, B., Milosavljevic, A.R., Scheier, P., Märk, T.D., Illenberger, E., (2006) J. Chem. Phys., 125, p. 044304. , JCPSA6 0021-9606 10.1063/1.2222370Palmer, M.H., Walker, I.C., Ballard, C.C., Guest, M.F., (1995) Chem. Phys., 192, p. 111. , CMPHC2 0301-0104 10.1016/0301-0104(94)00386-OTakatsuka, K., McKoy, V., (1984) Phys. Rev. A, 30, p. 1734. , PLRAAN 1050-2947 10.1103/PhysRevA.30.1734Bettega, M.H.F., Ferreira, L.G., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 1111. , PLRAAN 1050-2947 10.1103/PhysRevA.47.1111Da Costa, R.F., Da Paixão, F.J., Lima, M.A.P., (2005) J. Phys. B, 38, p. 4363. , 0022-3700Bachelet, G.B., Hamann, D.R., Schlüter, M., (1982) Phys. Rev. B, 26, p. 4199. , PRBMDO 0163-1829 10.1103/PhysRevB.26.4199Bettega, M.H.F., Natalense, A.P.P., Lima, M.A.P., Ferreira, L.G., (1996) Int. J. Quantum Chem., 60, p. 821. , 0020-7608Chaudhuri, P., Varella N. Do, M.T., De Carvalho, C.R.C., Lima, M.A.P., (2004) Phys. Rev. A, 69, p. 042703. , PLRAAN 1050-2947 10.1103/PhysRevA.69.042703Hunt, W.J., Goddard, W.A., (1969) Chem. Phys. Lett., 3, p. 414. , CHPLBC 0009-2614 10.1016/S0009-2614(99)00340-1Wan, J., Meller, J., Hada, M., Ehara, M., Nakatsujia, H., (2000) J. Chem. Phys., 113, p. 7853. , JCPSA6 0021-9606 10.1063/1.1316034Giuliani, A., Hubin-Franskin, M.-J., (2001) Int. J. Mass Spectrom., 205, p. 163. , 1387-3806Allan, M., Bauschlicher, C.W., (1980) J. Chem. Phys., 72, p. 880. , JCPSA6 0021-9606 10.1063/1.439243Winstead, C., McKoy, V., Bettega, M.H.F., (2005) Phys. Rev. A, 72, p. 042721. , PLRAAN 1050-2947 10.1103/PhysRevA.72.04272

Spin Exchange In Elastic E-o2 Collisions

Recent experiments using polarized electron beams have shown that spin-exchange effects for elastic collisions with O2 and NO are much smaller than for Na atoms. We report calculated spin-flip differential cross sections for elastic collisions of polarized electrons with O2 in agreement with experiment. In general, we can attribute large variations of the spin-flip differential cross sections to resonances and interference effects. Such features arising from interference, however, may be washed out in the molecular case due to the average over orientations. Calculations with oriented O2 show strong exchange effects as for Na.68111698170

The thickness of the cortical bone in different maxillae using medical images

The aim of this study was to investigate whether there is a relationship between the thickness of the cortical bone of mandible human and the age and the sex of patient. In this work the measure of the cortical bone thickness was obtained in different computed tomography (CT). Different human mandibles were scanned using high resolution micro-CT instrument in which many axial slices were obtained. A total of four medical images were studied and observed. Two different groups were characterized. The first one, with two female maxillae (F): an old and a young patient. The second group of two males mandibles (M), with similar age. A comparison between the male and female sex was also obtained. The cortical bone thickness of the mandible may be affected by tooth extraction, age and sex patient. The use of this type of information is useful for complementary diagnostic information and treatment planning

Electronic Excitation Of H2 By Electron Impact Using Soft Norm-conserving Pseudopotentials

We calculate electronic excitation cross sections for the b 3∑u + a 3∑g + c 3∏u, and d 3∏u states of H2 by electron impact. Our results were obtained with the Schwinger multichannel method with pseudopotentials and real potentials at the two-channel level of approximation. Pseudo-H atoms are used to generate H2 molecules with almost the same low-energy spectrum as the real molecules. We show that the dynamics of the electronic excitation process of the pseudomolecules by electron impact is very similar to the real case. Our results support the idea that pseudopotentials can be used to obtain reliable molecular electronic excitation cross sections by low-energy electron impact, confirming the expectations of previous studies with CH2O and HBr.54654355437Takatsuka, K., McKoy, V., (1981) Phys. Rev. A, 24, p. 2473(1984) Phys. Rev. A, 30, p. 1734Bettega, M.H.F., Ferreira, L.G., Lima, M.A.P., (1993) Phys. Rev. A, 47, p. 1111Natalense, A.P.P., Bettega, M.H.F., Ferreira, L.G., Lima, M.A.P., (1995) Phys. Rev. A, 52, pp. R1Bettega, M.H.F., Natalense, A.P.P., Lima, M.A.P., Ferreira, L.G., (1995) J. Chem. Phys., 103, p. 10566Rescigno, T.N., McCurdy, C.W., (1996) J. Chem. Phys., 104, p. 120Rescigno, T.N., (1996) J. Chem. Phys., 104, p. 125Hamann, D.R., Schlüter, M., Chiang, C., (1979) Phys. Rev. Lett., 43, p. 1494Christiansen, P.A., Lee, Y.S., Pitzer, K.S., (1979) J. Chem. Phys., 71, p. 4445Topp, W.C., Hopfield, J.J., (1973) Phys. Rev. B, 7, p. 1295Bachelet, G.B., Hamann, D.R., Schlüter, M., (1982) Phys. Rev. B, 26, p. 4199Bettega, M.H.F., Natalense, A.P.P., Lima, M.A.P., Ferreira, L.G., (1996) Int. J. Quantum Chem., 60, p. 821Goddard III, W.A., Hunt, W.J., (1974) Chem. Phys. Lett., 24, p. 464Kolos, W., Wolniewicz, L., (1965) J. Chem. Phys., 43, p. 2429Kolos, W., Wolniewicz, L., (1968) J. Chem. Phys., 48, p. 3672Browne, J.C., (1964) J. Chem. Phys., 40, p. 43Lee, M.T., Machado, L.E., Brescansin, L.M., Meneses, G.D., (1991) J. Phys. B, 24, p. 509Lima, M.A.P., Gibson, T.L., McKoy, V., Huo, W.M., (1988) Phys. Rev. A, 38, p. 4527. , and references cited therei

Electron Scattering From Molecules: Applications Of The Schwinger Multichannel Method To E--co And E--c2h 4 Collisions

To illustrate our recent efforts to obtain electronic excitation cross sections of molecules by electron impact, we present in this paper results for the X 1Σ a 3Π and A 1Π transitions of CO obtained with the Schwinger multichannel method. Our results are in good agreement with other theoretical calculations, although not so good when compared with experiments. We also discuss the importance of inclusion of polarization effects to obtain electronic excitation cross sections of some molecules through an example using the C2H4 molecule, which has a triplet state with a low-energy threshold. Finally, we present a very simple rule to estimate integral electronic excitation cross sections using the differential cross section (DCS) at 900, which can be useful to experimentalists using apparatus with difficulties to measure the DCS's at angles around 0 and 180 degrees. We show its efficiency for the present electronic excitation of the C2H4 molecule by electron impact. © 2007 IOP Publishing Ltd.881Garscadden, A., (1992) Z. Phys., 24 (2), pp. 97-99Boudaïffa, B., Cloutier, P., Hunting, D., Huels, M.A., Sanche, L., (2000) Science, 287 (5458), pp. 1658-1660Da Costa, R.F., Da Paixão, F.J., Map, L., (2004) J. Phys. B: At. Mol. Phys., 37 (6), pp. 129-L135Da Costa, R.F., Da Paixão, F.J., Map, L., (2005) J. Phys. B: At. Mol. Phys., 38 (24), pp. 4363-4378Da Costa, R.F., Map, L., (2006) Int. J. Quantum Chem., 106 (13), pp. 2664-2676Nonum Da Costa, R.F., Map, L., (2007) Phys. Rev., 75, p. 022705Sun, Q., Winstead, C., McKoy, V., Lima, M.A.P., (1992) J. Chem. Phys., 96 (5), pp. 3531-3535Rescigno, T.N., Schneider, B.I., (1992) Phys. Rev., 45 (5), pp. 2894-2902Takatsuka, K., McKoy, V., (1981) Phys. Rev., 24 (5), pp. 2473-2480Takatsuka, K., McKoy, V., (1984) Phys. Rev., 30 (4), pp. 1734-1740Chaudhuri, P., Varella Do, T.M.N., Carvalho, C.R.C., Map, L., (2004) Nucl. Instrum. Methods Phys. Res., 221, pp. 69-75Chaudhuri, P., Varella Do, T.M.N., Carvalho, C.R.C., Map, L., (2004) Phys. Rev., 69, p. 042703Lane, N.F., (1980) Rev. Mod. Phys., 52 (1), pp. 29-119Sun, Q.Y., Winstead, C., McKoy, V., (1992) Phys. Rev., 46 (11), pp. 6987-6994Morgan, L.A., Tennyson, J., (1993) J. Phys. B: At. Mol. Opt. Phys., 26 (15), pp. 2429-2441Lee, M.-T., MacHado, A.M., Fujimoto, M.M., MacHado, L.E., Brescansin, L.M., (1996) J. Phys. B: At. Mol. Opt. Phys., 29 (18), pp. 4285-4301Furlong, J.M., Newell, W.R., (1996) J. Phys. B: At. Mol. Opt. Phys., 29 (2), pp. 331-338Leclair, L.R., Trajmar, S., (1996) J. Phys. B: At. Mol. Opt. Phys., 29 (22), pp. 5543-5566Zetner, P.W., Kanik, I., Trajmar, S., (1998) J. Phys. B: At. Mol. Opt. Phys., 31 (10), pp. 2395-2413Trajmar, S., Szabo, A., Ostlund, N.S., (1989) Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory, pp. 194-197Da Costa, R.F., Bettega, M.H.F., Lima, M.A.P., Van Veen, E.H., (1976) Chem. Phys. Lett., 41 (3), p. 540Asmis, K.R., Allan, M., (1997) J. Chem. Phys., 106 (17), pp. 7044-7046Da Costa, R.F., Bettega, M.H.F., Lima, M.A.P., Da Costa, R.F., Bettega, M.H.F., Lima, M.A.P.

Cross Sections And Photoelectron Asymmetry Parameters For Photoionization Of H2o

The iterative Schwinger variational method is used to obtain cross sections and photoelectron asymmetry parameters for photoionization of the three outermost valence orbitals (1b1, 3a1, and 1b2) of H2O for photon energies from near threshold to 50 eV. A comparison of these calculated results with available experimental data is encouraging. © 1990 American Institute of Physics.9242362236

Comparative Study Of Electron And Positron Scattering By H2: The Role Of The Σg+2 Feshbach Resonance

We report two-channel calculations for e± - H2 scattering (X Σg+1 →X Σg+1, B Σu+3 for electrons and X Σg+1 →X Σg+1, B Σu+1 for positrons). We provide independent estimates of the electron Σg+2 Feshbach resonance (though for a limited range of interatomic distances) in good agreement with benchmark calculations. Resonance enhanced vibrational excitation cross sections were obtained with a time-dependent local complex potential approach and compare favorably with recent calculations and experimental data. The time resolution also provides good physical insight into the transient dynamics. In a previous work, we predicted the existence of a positron-hydrogen Σg+2 Feshbach resonance based on a fixed-nuclei scattering calculation (equilibrium geometry) that was not observed experimentally. 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Superelastic Cross Sections In E--h2 Scattering

We present superelastic cross sections of H2 by electron impact. Our results, obtained with the Schwinger multichannel method, include cross sections for the c 3Πu→ X 1Σg (+), c 3Πu→ b 1Σu (+), c 3Πu→ a 3Σg (+), and elastic c 3Πu→ c 3Πu transitions. The calculated cross sections are very large, indicating their importance in the modeling of discharge environments. We also investigate the dependence of these cross sections on the internuclear separation of the H atoms and on different approximations of the target wave function. To assess the role of the exchange potential in these processes, we also present the corresponding polarization fractions.55432433246Garscadden, A., (1992) Z. Phys. D, 24, p. 97Pinnaduwage, L.A., Christoforou, L.G., (1993) Phys. Rev. Lett., 70, p. 754Pinnaduwage, L.A., Christoforou, L.G., (1994) J. Appl. Phys., 76, p. 46Allan, M., Wong, S.F., (1978) Phys. Rev. Lett., 41, p. 1791Wadehra, J.M., Bardsley, J.N., (1978) Phys. Rev. Lett., 41, p. 1795Buckman, S.J., Elford, M.T., Newman, D.S., (1987) J. Phys. B, 20, p. 5175Christoforou, L.G., Datskos, P.G., Carter, J.G., (1991) Chem. Phys. Lett., 186, p. 11Burrow, P.D., Davidovits, P., (1968) Phys. Rev. Lett., 21, p. 1789Hall, R.I., Trajmar, S., (1975) J. Phys. B, 8, pp. L293Christoforou, L.G., Illenberger, E., (1993) Phys. Lett. A, 173, p. 78Capitelli, M., Colonna, G., Hassouni, K., Gicquel, A., (1994) Chem. Phys. Lett., 228, p. 687Takatsuka, K., McKoy, V., (1981) Phys. Rev. A, 24, p. 2473Beutler, H., Deubner, A., Junger, H.O., (1935) Z. Phys., 98, p. 181Gillan, C.J., Nagy, O., Burke, P.G., Morgan, L.A., Noble, C.J., (1987) J. Phys. B, 20, p. 4585Rescigno, T.N., McCurdy, C.W., Schneider, B.I., (1989) Phys. Rev. Lett., 63, p. 248Da Paixão, F.J., Lima, M.A.P., McKoy, V., (1992) Phys. Rev. Lett., 68, p. 1698Da Paixão, F.J., Lima, M.A.P., McKoy, V., (1996) Phys. Rev. A, 53, p. 1400Ferreira, L.G., private communicationBettega, M.H.F., Natalense, A.P.P., Lima, M.A.P., Ferreira, L.G., (1996) Int. J. Quantum Chem., 60, p. 821Goddard III, W.A., Hunt, W.J., (1974) Chem. Phys. Lett., 24, p. 464Lima, M.A.P., Gibson, T.L., McKoy, V., Huo, W.M., (1988) Phys. Rev. A, 38, p. 4527Steven, D., Parker, C., McCurdy, W., Rescigno, T.N., Lengsfield III, B.H., (1991) Phys. Rev. A, 43, p. 3514Linder, F., Schmidt, H., (1971) Z. Naturforsch. Teil A, 26, p. 1603Srivastava, S.K., Chatujian, A., Trajmar, S., (1975) J. Chem. Phys., 63, p. 2659Hegeman, T., Oberste-Vorth, M., Vogts, R., Hanne, G.F., (1991) Phys. Rev. Lett., 66, p. 2968Nordbeck, R.-P., Fullerton, C.M., Woeste, G., Thompson, D.G., Blum, K., (1994) J. Phys. B, 27, p. 537