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New Collision Data for H/H 2 and C x H y Databases

New Collision Data for H/H 2 and C x H y Databases. R.K.Janev Macedonian Academy of Sciences and Arts, Skopje, Macedonia. Scope:. Resonant vibrational excitation and dissociative attachment in e-H 2 in 11-14 eV region;

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New Collision Data for H/H 2 and C x H y Databases

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  1. New Collision Data for H/H2 and CxHy Databases R.K.Janev Macedonian Academy of Sciences and Arts, Skopje, Macedonia

  2. Scope: • Resonant vibrational excitation and dissociative attachment in e-H2 in 11-14 eV region; • Mutual neutralization in slow collisions of H- with H2+ and H3+ ions; • Electron impact excitation of X→ A and X→B transitions in CH • Dissociative excitation and ionization in e + CHy+collisions

  3. RVE and DEA in e+H2 in 11-14 eV collisions • Processes: e + H2(X1Σg+;v=0) → H2-(2Σg+) → → H2(X1Σg+;v) + e (RVE) → H- + H(n=2) (DEA) • Theoretical approach: - Resonance theory - Local complex potential approximation

  4. Elements of calculations

  5. LCA →Non-local integro-differential Eq. for ζ(R) In the local complex potential approximation this equation becomes (after separating the angular part):

  6. H2¯ energy parameters V ¯(R) : H2¯ (2Σg+) potential energy curve Г(R) : decay width of H2¯ (2Σg+) state Information on V ¯(R) and Г(R) from Stibbe andTennyson (1998;J.Phys.B) with suitable extrapolations

  7. RVE cross sections Chang, 1977; Herzenberg, 1979

  8. 2. Dissociative electron attachment Equations for ζi(R) in the LCA approximation are the same as in the RVE case Cross section:

  9. 3.Mutual neutralization in slow H2+,H3+ - H- collisions • H2+(1sσg) +H-(1s2)→H2(1sσg;nλσg)+H(1s) Radial coupling selection rule: Overall symmetry of initial and final states in reaction a) should be the same: → 1,3Σg+ final states of H2 Strong radial coupling of initial (ionic) and final (covalent) states exists only for exothermic channels: → n ≤ 3 →Final H2 states: X,EF,GK,HH (singl.) , a, h, g (tripl.)

  10. Schematic potential energy diagram (at large distances)

  11. Theoretical model • Multichannel Landau-Zener model (probability flux accumulation along various reaction paths for a given exit channel) • Landau-Zener two-state transition probability in the strong interaction region (around Rx)

  12. H3+ + H- • D3h symmetry for H3+ and H3* states • Initial state: H3+[(1sa1’)2 A1’] + H-(1s2) (i) • Final states with same symmetry as (i): • H3[(1sa1’2 nla1’)A1’] + H(1s) • Reaction exothermicity condition selects the first four A1’ states of H3*

  13. Computational method • Multichannel Landau-Zener (LZ) model • LZ two-state transition probability • Asymptotically exact ionic-covalent electron exchange interaction

  14. Radiative and predissociation decay of H3* states • H3*(nl;A1’)→ (intermediary state)→ … H3[(1sa1’)2(2pe’)E’]→H2(X1Σg+) + H(1s) →3H(1s) (Ground state of H3 is degenerate in the FC region of H3+ with two energy branches at large R; Yahn-Teller system)

  15. 4. Dissociative excitation and ionization of CDy+ by e-impact Processes: e + CDy+→ e + I+ + neutrals (DE) (y=1-4) e + CDy+ → 2e + I1+ +I2+ + neutrals (DI) • Recent total cross section measurements for specific ion production, σtot(DE+DI), and also σtot(DI) for D+ production; • Mesurements of total KER at a few energies • (Louvain-la-Neuve group; P.Defrance)

  16. Separation of channels • Determine channel thresholds from theoretical dissociation energies and observed KER spectra • Determine cross section points by integrating the KER peaks for a given channel at the corresponding energy • Use the inverse proportionality of cross section maximum with the threshold energy • Use the absolutely measured ionization cross section for H+ production and empirical scaling rule for the linearity of DE+ and DI+ fragments with the number of D atoms in CDy+ at high energies

  17. Status: For all CDy+ ions DE+ and DI+ channels have been separated For each of the DE+ or DI+ ion production channels the neutral fragmentation sub-channels have also been separated All the DE+ and DI+ channel cross sections have been fitted to (relatively) simple analytic fit functions

  18. 5. e-impact excitation of X→A and X→B transitions of CH • Computational method: - Born approximation for dynamics - Ab initio calculation of dipole moments • vi-vf resolved transitions • Predissociation included • Calculations of transitions to higher states also planned

  19. Bethe-Born formula

  20. Contributors: • R. Celiberto (Politechnico di Bari) • J. Wadehra (Wayne Univ., Detroit) • P. Defrance, J. Lecointre, et al. (Univ. Catholique de Louvain-la-Neuve) • J.G.Wang, C.L.Liu (IAPCM, Beijing)

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