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Electron collisions with the CF x radicals using the R -matrix method

Electron collisions with the CF x radicals using the R -matrix method. Iryna Rozum University College London Supervisors: Prof. J. Tennyson and Prof. N.J. Mason. CONTENT. Introduction The R -matrix method Electron collisions with the CF Electron collisions with the CF 2

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Electron collisions with the CF x radicals using the R -matrix method

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  1. Electron collisions with the CFx radicals using the R-matrix method Iryna Rozum University College London Supervisors: Prof. J. Tennyson and Prof. N.J. Mason

  2. CONTENT • Introduction • The R-matrix method • Electron collisions with the CF • Electron collisions with the CF2 • Electron collisions with the CF3 • Conclusions • Acknowledgement

  3. Introduction extremely high global warming potential C2F6and CF4 practically infinite atmospheric lifetimes CF3Ilow global warming potential C2F4strong source of CFx radicals new feedstock gases no information on how they interact with low E e– CFx radicals highly reactive, difficult species to work with in labs Theoretical approaches – attractive source of information

  4. Introduction Joint experimental and theoretical project e– interactions with the CF3I and C2F4 e– collisions with the CF, CF2 and CF3 N. Mason, P. Limao-Vieira and S. Eden I. Rozum and J. Tennyson

  5. Outer region e– Inner region C F Inner region: exchange electron-electron correlation multicentre expansion of  Outer region: exchange and correlation are negligible long-range multipolar interactions are included single centre expansion of  The R-matrix approach C R-matrix boundary r = a

  6. The R-matrix approach Total (N+1)-electron inner region wavefunction: kN+1= AIIN(x1,…,xN) jj(xN+1)aIjk + mm(x1,…,xN,xN+1)bmk(1) A is the anti-symmetrization operator, xn is the spatial and spin coordinate of the nth electron, j is a continuum orbital spin-coupled with the scattering electron, aIjk and bmkare variational parameters. First summation - ‘target + continuum’ configurations. Second summation -correlation or ‘L2’ term.

  7. Resonances • A resonance can be described as a long-lived metastable state of the target molecule, where the scattering e– is temporarily captured. • Breit -Wigner profile (E) = i tan-1[ires/ (E - Eires)] + + ai(E)i (2) (E) is the eigenphases sum, res is the resonance width, Eres is the resonance position, ai(E) is the background.

  8. Steps of calculations N-electron target calculations target parameters MO (N+1)-electron calculations Inner region (N+1) vectors Outer region Calculation of scattering parameters

  9. Electron collisions with the CF Target model • X1, 4–, 2+, 2, 2– and 4 • Slater type basis set: (24,14) + (,) valence target states2+ Rydberg state valence NORydberg NO () (24,14)(7…14 3…6) 2.44 ao C F single + double excitation single excitation (12)4(3 …6 1 2)11 (12)4(3 …6 1 2)10(73)1 final model

  10. Electron collisions with the CF Scattering model • R-matrix radius a = 13 a0 • range of scattering energies < 10 eV • ‘L2’ term: (12)4(3 …6 12 )12 (12)4(3 …6 1 2)11(73)1 • Stretch of C-F bond from 1.8 a0 to 3.6 a0 C F a = 13 ao

  11. Electron collisions with the CF Results • 2+ at R = 2.6 a0 - avoided crossing with 2 2+ • 4 - Rydberg-like?

  12. Electron collisions with the CF • total elastic cross section • electron impact excitation cross sections

  13. Electron collisions with the CF • Resonances 1Ee = 0.91 eV e = 0.75 eV 1+Ee = 2.19 eV e = 1.73 eV 3–Ee~ 0 eV 22

  14. Electron collisions with the CF • Bound states 1 Eb(Re) = 0.23 eV 3 Eb(Re) = 0.26 eV shape resonances E(1) = 0.054 eV E(3) = 0.049 eV 3– at R > 2.5 a0 1 at R > 3.3 a0 • 3– and 3 C(3P) + F–(1S) 1 and 1 C(1D) + F–(1S) unbound at R = 2.6 a0 27 become bound

  15. Electron collisions with the CF2 Target model • Gaussian basis set • state averaged NO • final model: (1a12a11b2)6(3a1…7a11b12b12b2…5b21a2)18 C 2.49 ao 103.8o F1 F2 a =10 ao

  16. Electron collisions with the CF2 Results • potential energy curves — no data are available

  17. Electron collisions with the CF 2 • electron impact excitation cross sections • total elastic cross sections

  18. Electron collisions with the CF 2 Resonances • shape resonances: 2B1(2A’’) Ee=0.95 eV e = 0.18 eV 2A1(2A’) Ee= 5.61 eV e = 2.87 eV • bound state at R > 3.2 a0 2B1 CF(2P) + F–(1S) 3b1 7a1

  19. Electron collisions with the CF3 C F3 110.7o F1 F2 Target representation • Cs symmetry group • X2A’, 12A”, 22A’, 22A”, 32A’, 32A” • Models 1. (1a’2a’3a’1a”)8 (4a’…13a’2a”…7a”)25 240 000 CSF (Ra) 2. (1a’…6a’1a”2a”)16 (7a’…13a’3a”…7a”)17 28 000 CSF 3. (1a’…5a’1a”2a”)14 (6a’…13a’3a”…7a”)19 50 000 CSF 2.53 ao a = 10 ao

  20. Target parameters MOLPRO CASSCF R-matrix codes R-matrix calculations Electron collisions with the CF3 E(x2A’) = -336.290 Eh (x2A’) = 0.51 Debye (12A”) = 7.91 eV (22A’) = 8.66 eV (22A”) = 8.66 eV (32A’) = 9.72 eV (22A”) = 9.72 eV CASSCF NO state-averaged NO

  21. Total elastic cross section Electron collisions with the CF3

  22. Electron collisions with the CF3 Electron impact excitation cross sections • Bound state E(1A’) ~ 0.6 eV

  23. Conclusion • First calculations on electron collisions with the CFx. • A new approach for treating of molecules with Rydberg states within R-matrix method. • Target parameters for the CF and CF2 are in good agreement with the data. • First vertical excitations energies for the CF3. • Total elastic and electron impact excitation cross sections. • Shape resonances were fitted. • Bound states were detected. • Our results should be reliable for the energies above 100 meV (previous studies of Baluja et al 2001 on OClO).

  24. Acknowledgement Prof. Jonathan Tennyson Prof. Nigel Mason Natalia Vinci and Jimena Gorfinkiel

  25. Introduction Joint experimental and theoretical project e– interactions with the CF3I and C2F4 e– collisions with the CF, CF2 and CF3 N. Mason, P. Limao-Vieira and S. Eden I. Rozum and J. Tennyson

  26. Scheme of calculations Integral evaluation Configuration generation Hamiltonian construction and diagonalization Inner region Outer region Calculation of scattering parameters

  27. Electron collisions with the CF2 Results • target parameters: (X1A1) = 0.448 D exp(X1A1) = 0.469 ± 0.026 D (Kirchhoff and Lide 1973) (3B1) = 2.49 eV (3B1) = 2.42 eV (Cai 1993) • potential energy curves

  28. Electron collisions with the CF Results • target properties (X2) = 0.64 D exp(X2) = 0.645 ± 0.014 D (Saito et al 1983) (2+) = 5.65 eV (2+) = 5.65 eV (Petsalakis 1999) • potential energy curves

  29. Electron collisions with the CF3 C F3 110.7o F1 F2 Target representation 1. (1a’2a’3a’1a”)8 (4a’…13a’2a”…7a”)25 2. (1a’…5a’1a”2a”)14 (6a’…13a’3a”…7a”)19 3. (1a’…6a’1a”2a”)16 (7a’…13a’3a”…7a”)17 2.53 ao MOLPRO CASSCF R-matrix codes R-matrix target calculations a = 10 a0 CASSCF NO state-averaged NO

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