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Alignment, orientation and conformational control: Applications in ultrafast imaging

Alignment, orientation and conformational control: Applications in ultrafast imaging. Henrik Stapelfeldt. Department of Chemistry University of Aarhus Denmark. Ultra-fast Dynamic Imaging of Matter II April 30 – May 3, 2009. Purpose of this talk.

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Alignment, orientation and conformational control: Applications in ultrafast imaging

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  1. Alignment, orientation and conformational control: Applications in ultrafast imaging Henrik Stapelfeldt Department of Chemistry University of Aarhus Denmark Ultra-fast Dynamic Imaging of Matter II April 30 – May 3, 2009

  2. Purpose of this talk Recent progress in laser based alignment, orientation and conformer selection methods List potential examples of ultrafast dynamic imaging

  3. 1-D Alignment Order of the molecular geometry with respect to a space fixed axis

  4. 1-D Alignment Order of the molecular geometry with respect to a space fixed axis

  5. 3-D Alignment 3-dimensional order of the molecular geometry Z Y X

  6. 3-D Orientation 1-D Orientation Breaking the head for tail symmetry

  7. How to align molecules • Use an intense (but not too intense) nonresonant pulse • and rotationally cold molecules • Long pulse  Adiabatic alignment • Short pulse  Nonadiabatic alignment • (transient / impulsive)

  8. Classical picture of alignment Potential energy - Linear molecule - Strong, linearly polarized laser field, High rotational energy  Low rotational energy

  9. Quantum Mechanical picture of alignment  Solve the rotational Schrödinger equation Zon (1976), Friedrich + Herschbach (1995), Seideman (1995) Pendular states : linear combination of field free rotational states For a linear molecule :

  10. Adiabatic alignment  slow turn-on of the alignment field Alignment pulse = nanosecond pulse Pendular states Field-free states J = 2 J = 1 32 30 J = 0 22 20 21 11 10 00

  11. light F+ I+ F+ C6H3n+ Measurement of the spatial orientation of the molecules Coulomb explosion : light n+ m+

  12. Experimental Setup I+ I+ Supersonic expansion Alignment pulse YAG : 9 ns 1064 nm Molecular beam 25 fs ionization pulse 2-D ion detector CCD camera

  13. 1D Alignment of iodobenzene (C6H5I) I+ images

  14. 1D Alignment of Iodobenzene (C6H5I) intensity and temperature dependence

  15. 1D Alignment of 4,4’ dibromobiphenyl (C12H8Br2) Br+ images

  16. 3D alignment  Elliptically polarized long pulse Larsen et al. PRL 2000 Tanji et al. PRA 2005  Perpendicularly-polarized pulse pair Lee et al. PRL 2006 Viftrup et al. PRL 2007  Short elliptically polarized long pulse Rouzée et al. PRA 2008

  17. 3D alignment - Elliptically polarized long pulse 2,6 dFIB End-view I+ F+

  18. Rotational state selection of polar molecules by electrostatic deflection Strongly improved laser induced orientation and alignment

  19. EYAG  Es Setup and idea

  20. Deflection of iodobenzene 10 kV 5 kV 0 kV

  21. Alignment and orientation of iodobenzene  = 90 100 110 120 135 150 EYAG  I+ - C6H52+ I+ - C6H5+ Estatic  = 90 80 70 60 45 30 EYAG  Estatic EYAG Undeflected molecules  = 90 100 110 120 135 150  Estatic EYAG  = 90 80 70 60 45 30  Estatic

  22. Alignment and orientation of iodobenzene  = 90 100 110 120 135 150 EYAG  I+ - C6H52+ I+ - C6H5+ Estatic  = 90 80 70 60 45 30 EYAG  Estatic EYAG  = 90 100 110 120 135 150  Estatic EYAG  = 90 80 70 60 45 30  Estatic

  23. Improved alignment

  24. Alignment and orientation of iodobenzene  = 90 100 110 120 135 150 EYAG  I+ - C6H52+ I+ - C6H5+ Estatic  = 90 80 70 60 45 30 EYAG  Estatic EYAG Undeflected molecules  = 90 100 110 120 135 150  Estatic EYAG  = 90 80 70 60 45 30  Estatic

  25. Orientation by mixed fields Combine static electric field and laser field 1999: Friedrich + Herschbach 2001: Buck 2003: Sakai 2> Laser induced potential 1> Static electric field mixes the pendular states: ”+” combination: 2> + 1>  localization at  = 0o “-” combination: 2> - 1>  localization at  = 180o

  26. BUT ! Different initial states orient in opposite directions Averaging over the Boltzman distribution strongly diminishes the overall degree of orientation Ideal target: All the molecules initially populated in the rotational ground state [or in the same rotational state (Marc Vrakking, Nat. Phys. 2009)]

  27. Up-down asymmetry Phys. Rev. Lett. 102, 023001 (2009)

  28. Deflection of iodobenzene seeded in He or in Ne F. Filsinger et al., arXiv:0903.5413v1 (2009)

  29. Up-down asymmetry F. Filsinger et al., arXiv:0903.5413v1 (2009)

  30. Details of rotational quantum states

  31. Latest improvements capacitor plates

  32. 3D alignment - Elliptically polarized long pulse 1:2 1:4 Linear 2,6 dFIB

  33. 3D alignment - Elliptically polarized long pulse 1:2 1:4 Linear Undeflected 2,6 dFIB Deflected

  34. 3D orientation See also: Sakai, PRA (2005) Undeflected Deflected

  35. Conformer selection

  36. Cis and trans conformers of 3-aminophenol trans-3AP cis-3AP p = 2.3 D p = 0.7 D

  37. Selective probing of cis and trans (REMPI) Ip S1 S0

  38. Cis / transconfomer selection Cis fraction

  39. Anti and gauche conformers of 1,2-diiodoethane (C2H4I2) anti gauche Side-view End-view p ~ 2 D p = 0 D

  40. Deflection of 1,2-diiodoethane

  41. 11.0mm 10.1mm 9.7mm YAG Cou 008 007 009 003 006 004+005 011 012 013 Coulomb explosion of 1,2-diiodoethane I+ images gauche anti Parallel fields Perpendicular fields

  42. CONCLUSIONS  1D and 3D aligned or oriented molecules are available for experiments  Adiabatic alignment provides strongest alignment and orientation BUT it is not field-free conditions  rapid truncation of alignment field [Stolow PRL (2003), Sakai PRL (2008)]  Quantum state selection can strongly enhance the degree of (adiabatic) alignment and orientation and alignment / orientation can be induced at lower fields!  Electrostatic beam deflection  control of stereo isomers (conformers)

  43. OUTLOOK  Strong laser field phenomena - High harmonic generation - Electron diffraction  Selection of a single rotational quantum state (Marc Vrakking: NO and hexapole, Nat. Phys. March 2009)  Time resolved studies of chirality [PRL 102,/ 073007 (2009) ]  Steric effects in reactive scattering (SN2: Trippel and Wester)  Photoelectron angular distribution from fixed-in-space molecules [PRL 100, 093006 (2008) , Science 320, 1478 (2008) , Science 323, 1464 (2009)]  Aligned molecules as targets for free electron lasers - FLASH: Photoelectron spectroscopy (angular distributions) - LCLS: x-ray diffraction

  44. OUTLOOK • x-ray diffraction with free-electron laser sources Calculations by Henry Chapman

  45. X-ray diffraction from aligned molecules Calculations by Henry Chapman Planned target molecule

  46. Deflection project Fritz Haber Institute, Berlin Lotte Holmegaard Jens H. Nielsen Iftach Nevo Jonas L. Hansen Frank Filsinger Jochen Küpper Gerard Meijer

  47. Enjoy the silence

  48. Alignment beam Beam overlap at LCLS ! Molecular beam X-ray beam

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