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Soon to begin …. Michael Probst Sassari, September 27, 2007 Electron – Molecule Reactions: Quantum Chemistry of Electron Attachment to Biomolecules Institute.

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Presentation on theme: "Soon to begin …. Michael Probst Sassari, September 27, 2007 Electron – Molecule Reactions: Quantum Chemistry of Electron Attachment to Biomolecules Institute."— Presentation transcript:

1 soon to begin …

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

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

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

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... Astrophysics - reactions in space Radiation treatment

8 for example (3)... Semiconductor plasmas Nanotechnology and surface engineering

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

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

11 e e

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

13

14 Experimental result:

15 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.

16 N1 C6

17 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.

18 Example: Adenine

19 What we worked on … 2. Neutral and anionic energy surface – where do they cross ? 3. Why do similar molecules show different spectra ? 1. Which H dissociates most easily ? (calculations of BDE) (calculation of stable and metastable potential energy curves) (analysis of molecular orbitals)

20 1. Which H dissociates most easily ? BDESystem of H fromneutralanion C N C N QC calculations (G2(MP2) on adenine): BDESystem of H fromneutralanion C N C N

21 Extrapolation methods for BDE: Low qual. method Large basis set Low qual. method Small basis set High qual. method Large basis set High qual. method Small basis set Basis set energy correction Correlation energy correction (LL-LS)+ (HL-LS)

22 Extrapolation methods - G2: 6-11G(d,p)6-11+G(d,p)6-11G(2df,p)6-11+G(3df,2p) MP2IKLD MP4JBC QCISD(T)A X 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 ∆H f = ±1.59 kcal/mol = 0.06 eV

23 DBS (A-H) - +H  *(N(9)-H) 0 1 EA(A-H) - r(N(9)-H) (Å) E pot (eV) EA(P-H) - Mechanism of dissociation: Potential energy curves:

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

25

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

27 [A-H] - … H potential energy: E anion = E neutral + E electron E neutral are calculated from UB3LYP/aug-cc-pVTZ E electron are calculated from UOVGF/aug-cc-pVTZ

28 [A-H] … H:

29 E SOMO = f(r N9-H ) UOVGF/aug-cc-pVTZ

30 E SOMO = f(r N9-H ) Metastable part UOVGF/aug-cc-pVTZ

31 %q%q r[N9-H] = 1.3 Å Stabilise the anion by slightly increasing the nuclear charge. extrapolate.

32 E SOMO = f(r N9-H ) %q%q

33 +

34 [A-H] … H neutral and anionic curves:

35 Why do similar purine derivatives show different spectra ?

36 LUMO & Electrostatic potential: ESP: negative, positive PurineAdenineDimethyladenine

37 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)

38 Thank you …


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