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Department of Experimental Physics, Comenius University Bratislava , Slovakia

Department of Experimental Physics, Comenius University Bratislava , Slovakia. Formation of positive ions by electron impact: Temperature effects Š. Matejčík. Department of Experimental Physics. Division of plasma physics l ow temperature plasma

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Department of Experimental Physics, Comenius University Bratislava , Slovakia

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  1. Department of Experimental Physics, Comenius University Bratislava, Slovakia Formation of positive ions by electron impact: Temperature effects Š. Matejčík

  2. Department of Experimental Physics Division of plasma physics • low temperature plasma technological plasmas, glow discharges ... • high pressure discharges corona discharge, barrier discharge ... • reactions in the plasma electron impact ionization, electron attachment to the molecules ...

  3. Reactions in plasma • Electron interactions • Photon induced reactions • Ion –molecule reactions • Neutral reaction • Reactions on the surfaces

  4. Electron interactions in plasma • Electron impact ionization • Electron attachment • Excitation • Dissociation • Electron reaction on the surfaces

  5. Comenius university • Electron attachment • Electron impact ionization • Electron induced reactions on surfaces Preparation • Electron impact excitation

  6. Electron impact ionization: e + AB → AB+ + 2e Dissociative electron impact ionization: e + AB → A+ + B + 2e Ion pair formation: e + AB → A+ + B- + e Fusion related research Molecules: CH4, CH3D, CD4, C2H6, C3H8

  7. We have studied • appearance energies (AE) of the positive ions • gas temperature effects on the AE • isotopic effects on AE Theory: Ionization energies (OVGF, CCSD(T)) Appearance energies (G3, G3B3 and CBS-APNO, CBS-Q)

  8. Experimental setup: E = 0 – 150 eV FWHM ~50-140 meV Ie~20-100nA T = 293K 693K

  9. high Tg Electron impact ionization low Tg σ E

  10. Rate coefficient f(E,Te) high Tg low Tg σ E

  11. VIE AE AIE A+ IE A

  12. AE2 E f ΔAE = AE2-AE1= = Ei(T2)-Ei(T1) Ei(T)=Ev(T)+Er(T) AE1

  13. Sensitivity in present experiment: σ ~10-26 - 10-25 m2 σ E

  14. Problem of threshold energy estimation

  15. Threshold behaviour of the cross sections for EII Atoms: Wannier theory: w(E,AE,A,d) = 0 E<AE A(E-IE)d E>AE d=1.127 Fitting function: w(E,AE,A,d) f(E,U) - EEDF

  16. Threshold behaviour of the cross sections d=1.127±0.01

  17. Threshold behaviour of the cross sections for EII Molecules - empirical formula: w(E,AE1,AE2,d1,d2A) = 0 E<AE1 A(E-AE1)d1 E>AE1 A(E-AE2)d2 + A(E-AE1)d1E>AE2 ...

  18. Temperature effects on Appearance energies of the ions Predicted by: Rosenstock – review article Plessis&Marmet – in CH4 and C2H6 papers H. M. Rosenstock, Int. J. Mass Spectr. Ion Phys., 20 (1976)139 P. Plessis et al., Can. J. Chem. 65 (1987) 1424, J. Phys. B, 16 (1983) 1770

  19. CH4 e + CH4→ CH4+ + 2e CH3+ + H + 2e CH3+ + H- + 2e CH2+ + H2 + 2e CH+ + H2 + H+ 2e C+ + 2H2 + 2e ...

  20. 293K CH4+/CH4 693K

  21. Ei(T) - rotational and vibrational energy of the molecule at T Ei =Ei(693) – Ei(293 K) ~ 0.12 eV Stano et al., J. Phys. B: At. Mol. Opt. Phys. , 36 (2003) 261

  22. CH3+/CH4 293K 693K

  23. AE1=12.75 eV AE1=12.62 eV CH3D+/CH3D 293K 693K

  24. C2H6+/C2H6 293K 693K

  25. C2H6

  26. C3H8+/C3H8 293K 693K

  27. Summary Temperatures 293 and 693 K

  28. Isotopic effect on AE Changes in vibrational energies in isotopomers Heavy isotopomer – lower zero point energy => larger AE Comparison: CH4, CD4, CH3D

  29. Isotopic effect on AE

  30. Isotopic shift a) F. P. Lossing, A. W. Tickner, W. A. Bryce, J. Chem. Phys.19, 1254 (1951). b) V. H. Dibeler, M. Krauss, R. M. Reese, F. N. Harlee J. Chem. Phys.42, 3791 (1965).

  31. Conclusions experimentally observed dependence of AE´s on the temperature magnitude of the shift ~vibrational and rotational excitation of the molecule confirmed isotopic shift in the appearance energies of the molecules

  32. Contribution to new CRP • Experiment: • The temperature effects: • estimation of the partial cross sections in C3H8 for particular fragment ions • - evaluation of the rate coefficients • Theory - QM: • - BenHm - electronic structure, binding energies, volatility, ionization potentials and electron affinities • - H2 reactions with Ben

  33. Coworkers Comenius University Bratislava M. Stano, E. Vašeková, J.D. Skalný, D. Kubala, J. Kočíšek Theorists:I. Hubac, J. Urban, P. Mach S. Denifl, T.D. Märk University Innsbruck Support VW Stiftung, EU (Euroatom-FUSION), IAEA, APVT

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