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soon to begin …. Electron – Molecule Reactions: Quantum Chemistry of Electron Attachment to Biomolecules. Michael Probst. Institute of Ion Physics and Applied Physics, Innsbruck University, Technikerstraße 25, 6020 Innsbruck, Austria. Sassari, September 27, 2007. Collaboration with:.

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  1. soon to begin …

  2. Electron – Molecule Reactions:Quantum Chemistry of Electron Attachment to Biomolecules Michael Probst Institute of Ion Physics and Applied Physics, Innsbruck University, Technikerstraße 25, 6020 Innsbruck, Austria Sassari, September 27, 2007

  3. Collaboration with: • Natcha Injan, Jumras Limtrakul • Stephan Denifl, Fabio Zappa, Ingo Mähr, Manuel Beikircher,Sylwia Ptasinska,Tilmann Märkand Paul Scheier

  4. Electron – Molecule Reactions: Aim: Application and understanding of electron-driven processes

  5. electron-driven processes ... ... are dominant in many areas of basic and applied Science and Technology.

  6. for example (1) ... • Atmospheric physics and planetary atmospheres • Radiation damage of DNA and cellular material

  7. for example (2) - related to... • Radiation treatment • Astrophysics - reactions in space

  8. for example (3) ... • Nanotechnologyand surface engineering • Semiconductorplasmas

  9. Our topic is related to the 2nd... somewhat  • Radiation damage of DNA and cellular material

  10. ... but what does really happen ? e e

  11. ...but what does really happen ? e e

  12. Experimental setup ... hemispherical electron monochromator quadrupole mass filter oven channeltron SEM

  13. Experimental result:

  14. Typical mechanism • An electron is captured in a dipole – bound state. • It enters an antibonding * orbital to form a metastable anion that can weaken a N-H (or C-H) bond.

  15. C6 N1

  16. Suggested mechanism • An electron is captured in a dipole – bound state. • It enters an antibonding * orbital to form a metastable anion that can weaken a N-H (or C-H) bond. • H can dissociate and [M-H]- remains.

  17. Example: Adenine

  18. What we worked on … • Which H dissociates most easily ? (calculations of BDE) • Neutral and anionic energy surface –where do they cross ? (calculation of stable and metastable potential energy curves) • Why do similar molecules show different spectra ? (analysis of molecular orbitals)

  19. 1. Which H dissociates most easily ? QC calculations (G2(MP2) on adenine):

  20. Extrapolation methods for BDE: Low qual. methodLarge basis set High qual. methodLarge basis set Basis setenergycorrection (LL-LS)+ (HL-LS) Correlation energy correction Low qual. methodSmall basis set High qual. methodSmall basis set

  21. Extrapolation methods - G2: We want to arrive at X: E[+] = E[B] - E[J]; E[2df] = E[C] - E[J] 12= (E[D] - E[I]) - (E[K] - E[I]) - (E[L] - E[I]) = =E[D] + E[I] - E[K] - E[L] E[X] = E[A] + E[+] + E[2df] + 12 average error in ∆Hf = ±1.59 kcal/mol = 0.06 eV

  22. Mechanism of dissociation: Potential energy curves: s*(N(9)-H) Epot (eV) EA(A-H)- EA(P-H)- (A-H)-+H 1 0 DBS r(N(9)-H) (Å)

  23. Mechanism of dissociation:Potential energy curves: Can we calculate these curves ? • Neutral curve: YES • Stable part of the anionic curve: (excited state but below neutral curve) YES • Metastable part of the anionic curve X YES (above neutral): NO With extrapolation methods for the ‘metastable energy’ • Avoided crossing: YES (In principle easy, accuracy is difficult …)

  24. Mechanism of dissociation:Potential energy curves:

  25. Mechanism of dissociation:Potential energy curves: In principle, the probability of M + e- [M-H]- + H can be calculated from these curves ! (via tunneling rates; the accuracy is a problem)

  26. [A-H]- … H potential energy: Eanion = Eneutral + EelectronEneutral are calculated from UB3LYP/aug-cc-pVTZEelectron are calculated from UOVGF/aug-cc-pVTZ

  27. [A-H] … H:

  28. ESOMO = f(rN9-H) UOVGF/aug-cc-pVTZ

  29. ESOMO = f(rN9-H) Metastable part UOVGF/aug-cc-pVTZ

  30. r[N9-H] = 1.3 Å %q • Stabilise the anion by slightly increasing the nuclear charge. • extrapolate.

  31. %q ESOMO = f(rN9-H)

  32. ESOMO = f(rN9-H) +

  33. [A-H] … H neutral and anionic curves:

  34. Why do similar purine derivatives show different spectra ?

  35. LUMO & Electrostatic potential: ESP: negative, positive Purine Adenine Dimethyladenine

  36. Concluding … • Some (but not all) features of the DEA process can be predicted. • Ssummary of experimental and theoretical work published in Angew. Chemie IE 46, p.5238 (2007)

  37. Thank you …

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