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ELECTRON SPECTROSCOPY AND MASS SPECTROMETRIC STUDY OF PENNING IONIZATION OF MOLECULES

ELECTRON SPECTROSCOPY AND MASS SPECTROMETRIC STUDY OF PENNING IONIZATION OF MOLECULES. F. Vecchiocattivi Dipartimento d’Ingegneria Civile ed Ambientale Università degli Studi di Perugia Perugia - Italy. … it’s elementary, my dear Watson. The Penning ionization process …. (1894-1953).

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ELECTRON SPECTROSCOPY AND MASS SPECTROMETRIC STUDY OF PENNING IONIZATION OF MOLECULES

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  1. ELECTRON SPECTROSCOPY AND MASS SPECTROMETRIC STUDY OF PENNING IONIZATION OF MOLECULES F. Vecchiocattivi Dipartimento d’Ingegneria Civile ed Ambientale Università degli Studi di Perugia Perugia - Italy

  2. … it’s elementary, my dear Watson. The Penning ionization process …

  3. (1894-1953)

  4. F. M. Penning, Naturwissenschaften 15, 818 (1927) (1894-1953)

  5. A* + M A + M+ A + M+ + e- A* + M  (A…M)*  (A…M)+ + e-

  6. electron energy analyzer E target molecule beam source rare gas beam source electrons ions electron bombardment exciter quadrupole mass spectrometer

  7. Perugia molecular beam apparatus for Penning ionization studies beam crossing volume

  8. Ar+ 100 10 Ionization cross section (Å2) HeAr+ 3,3/2 He*(23S) + Ar  He + Ar+(2P3/2) + e- 1 3,1/2 He*(23S) + Ar  He + Ar+(2P1/2) + e- 0.01 0.1 1 1,3/2 He*(21S) + Ar  He + Ar+(2P3/2) + e- Collision energy (eV) 1,1/2 He*(21S) + Ar  He + Ar+(2P1/2) + e- He*(21S, 23S) + Ar He + Ar+(2P3/2, 2P1/2) + e-

  9. 3,3/2 = 2.1±0.2 3,1/2 B. Brunetti, P. Candori, S. Falcinelli, B. Lescop, G. Liuti, F. Pirani, F. Vecchiocattivi (2005) to be published

  10. He*(3S) + Ar  [He-Ar]* [He-M]+ + e- He*(3S) Ar+ Ar He    

  11. P P S He + Ar+(2P1/2) W=1/2 He + Ar+(2P3/2) W=3/2 W=1/2 The relative population of the J=1/2 and J=3/2 states of the Ar+ product practically reflects the  character of the final He-Ar+ state.

  12. Ne*(3P2,0) Ar+             Ne*(3P2,0) + Ar  [Ne-Ar]* [Ne-M]+ + e-

  13. Ar Ar Ne+ Ne+ e-  e-           symmetry  symmetry             e- e-   Ne Ne Ar+ Ar+

  14. + 2 + 2 Kr ( P ) Kr ( P ) 3/2 1/2 * 3 Ne ( P ) * 3 Ne ( P ) 2 2 * 3 Ne ( P ) E =0.050 eV 0 coll * 3 Ne ( P ) 0 1.8 2.0 2.2 2.4 2.6 2.8 3.0 electron energy (eV) B. Brunetti, P. Candori, S. Falcinelli, B. Lescop, G. Liuti, F. Pirani, F. Vecchiocattivi (2005) to be published

  15. J=2 (present experiment) 6 J=2 (Hotop and coworkers) Ne*(3P0) 5 J=0 (present experiment) J=0 (Hotop and coworkers) j,1/2 4 /Q j,3/2 3 Q 2 1 Ne*(3P2) 0 0.0 0.1 0.2 0.3 0.4 0.5 collision energy (eV)

  16. Penning ionization occurs through the transfer of an outer shell electron from the target particle into the inner shell vacancy of the metastable atom. The process is therefore governed by the mutual orientation of atomic orbitals. In the case of atom-molecule systems, this also implies a strong effect of the orientation of the target molecule.

  17. high voltage + - hexapole filter Ion detector CH3Cl beam rotatable plate Ar* beam Ar* + CH3Cl  CH3Cl+ + Ar + e- H.Ohoyama, H.Kawaguchi, M.Yamato, T.Kasai, B.G.Brunetti, F.Vecchiocattivi, Chem.Phys.Lett. 313, 484 (1999). H. Ohoyama, M.Yamato, S. Okada, T. Kasai, B. G. Brunetti, F. Vecchiocattivi, Phys.Chem.Chem.Phys. 3, 3598 (2001). B. G. Brunetti, P. Candori, S. Falcinelli, T. Kasai, H. Ohoyama, F. Vecchiocattivi, Phys.Chem.Chem.Phys. 3, 807 (2001). V. Aquilanti, F. Pirani, D. Cappelletti, F. Vecchiocattivi, T. Kasai, in: “Theory of chemical reaction dynamics”, Kluwer Academic, the Netherlands, p.243 (2004). V.Aquilanti, M. Bartolomei, F. Pirani, D. Cappelletti, F. Vecchiocattivi, Y. Shimizu, T. Kasai. Phys.Chem.Chem.Phys. 7, 291 (2005)

  18. Ar*

  19. Ar* CH3Cl  Ar* cos(g)=+1 Cl end cos(g)=-1 CH3 end cos(g)=0 0 -1 +1 cos (g) stereo-opacity 1.2 0.8

  20. Ne* + N2O stot s s N2O+ 10 NO+ s Cross Section (Å2) 1 O+ s NeN2O+ 0.1 0.1 0.2 Collision Energy (eV) Rg = He, Ne Rg* + N2O  [Rg…N2O+] + e- [Rg…N2O+]  N2O+  NO+ + N  O+ + N2  RgN2O+

  21. He*(23S, 21S)-N2O 0.12 0.10 0.08 Collision Energy (eV) 0.06

  22. Molecular orbitals of N2O HOMO LUMO Oxygen “lone pair” Nitrogen “lone pair”

  23. He* N2O+ ion in the ground 2 state N N O N2O+ ion in the excited 2 state He* N N O

  24. He*(21S) + N2O He*… NNO NNO … He*

  25. He*(3S) + H2O  He + H2O+ + e-77.9% He + OH+ + H + e-17.9% He + OH + H+ + e- 3.2% HeH+ + OH + e- 0.8% HeO+ + H2 + e- 0.2% Ne*(3P) + H2O  Ne + H2O+ + e-

  26. 1b1 Adiabatic Ionization Potential (2p non bonding orbital) He(3S) 19.82 eV 1b2 17.18 eV Ne(3P2) 16.62 eV 13.84 eV 3a1 1b1 12.62 eV 3a1 1b2 (sp2 lone pair orbital) (sp bonding orbitals)

  27. 1b1 He*(3S) + H2O (2p non bonding orbital) ~ X 2B1 (b1-1) ~ A 2A1 (a1-1) ~ B 2B2 (b2-1) 0 1 2 3 4 5 6 7 8 eV Electron energy 3a1 1b2 (sp2 lone pair orbital) (sp bonding orbitals)

  28. 1b1 Ne*(3P2) + H2O (2p non bonding orbital) ~ A 2A1 (a1-1) ~ X 2B1 (b1-1) 0 1 2 3 4 5 6 7 8 eV Electron energy 3a1 1b2 (sp2 lone pair orbital) (sp bonding orbitals)

  29. 60 * Ne -H O 2 50 ionization cross section (Å2) 40 30 0,03 0,1 0,2 collision energy (eV) B. Brunetti, P. Candori, S. Falcinelli, B. Lescop, G. Liuti, D. Malfatti, F. Pirani, F. Vecchiocattivi (2005) to be published

  30. 3a1 (sp2 lone pair orbital) 1b1 (2p non bonding orbital)

  31. Ne* + H2O ~ A (2A1) ~ X (2B1) Photoionization electron spectrum, energy scaled B. Brunetti, P. Candori, S. Falcinelli, B. Lescop, G. Liuti, D. Malfatti, F. Pirani, F. Vecchiocattivi (2005) to be published

  32. Ne* + H2O

  33. The Penning ionization of molecules strongly depends on the orientation of the molecule with respect to the approach direction of the metastable atom. The orientation not only affects the ionization probability, but also the specific reaction following the ionization event (dissociation, rearrangement, etc.)

  34. Optical Potential Model (H. Bethe, 1940): The Potential is assumed to be complex W(R) = V(R) – i/2 (R) and therefore the phase shift is also complex = + i

  35. Differential Cross Section: Integral Cross Section: Total Ionization Cross Section: B. Brunetti, F. Vecchiocattivi, Current Topic on Ion Chemistry and Physics, edited by C.Y. Ng, T. Baer, I. Powis (John Wiley & Sons Ltd, New York, 1993), p. 359

  36. J. Chem. Phys. 95, 1801 (1991) Differential elastic cross section Total ionization cross section Integral scattering cross section

  37. Dipartimento d’Ingegneria Civile ed Ambientale F. Biondini P. Candori S. Falcinelli G. Liuti D.Malfatti Dipartimento di Chimica V. Aquilanti B. Brunetti F. de Angelis F. Pirani F. Tarantelli

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