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 X Y Z

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 a)Long pulse  Adiabatic alignment b)Short pulse  Nonadiabatic alignment (transient / impulsive)

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

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

10. J = 2 J = 1 J = 0 Field-free states Pendular states 2121 2020 1010 0 1 3232 3030 2 Adiabatic alignment  slow turn-on of the alignment field Alignment pulse = nanosecond pulse

11. Measurement of the spatial orientation of the molecules m+m+ n+n+ Coulomb explosion : light I+I+ C 6 H 3 n+ light F+F+ F+F+

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

13. 1D Alignment of iodobenzene (C 6 H 5 I) I + images

14. 1D Alignment of Iodobenzene (C 6 H 5 I) intensity and temperature dependence

15. 1D Alignment of 4,4’ dibromobiphenyl (C 12 H 8 Br 2 ) 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 End-view I+I+ F+F+ 2,6 dFIB

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

19. Setup and idea EsEs E YAG 

20. Deflection of iodobenzene 0 kV 5 kV 10 kV

21.  = 90 100 110 120 135 150  = 90 80 70 60 45 30 I + - C 6 H 5 + I + - C 6 H 5 2+ E YAG E static  E YAG E static   = 90 100 110 120 135 150  = 90 80 70 60 45 30 Alignment and orientation of iodobenzene E YAG E static  E YAG E static  Undeflected molecules

22.  = 90 100 110 120 135 150  = 90 80 70 60 45 30 I + - C 6 H 5 + I + - C 6 H 5 2+ E YAG E static  E YAG E static   = 90 100 110 120 135 150  = 90 80 70 60 45 30 Alignment and orientation of iodobenzene E YAG E static  E YAG E static 

23. Improved alignment

24.  = 90 100 110 120 135 150  = 90 80 70 60 45 30 I + - C 6 H 5 + I + - C 6 H 5 2+ E YAG E static  E YAG E static   = 90 100 110 120 135 150  = 90 80 70 60 45 30 Alignment and orientation of iodobenzene E YAG E static  E YAG E static  Undeflected molecules

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

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 Linear 1:4 1:2 2,6 dFIB

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

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

35. Conformer selection

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

37. Selective probing of cis and trans (REMPI) S0S0 S1S1 IpIp

38. Cis / trans confomer selection Cis fraction

39. Side-view Anti and gauche conformers of 1,2-diiodoethane (C 2 H 4 I 2 ) End-view  p = 0 D antigauche  p ~ 2 D

40. Deflection of 1,2-diiodoethane

41. 11.0mm10.1mm9.7mm YAG Cou 008007009 003006004+00 5 011012013 Coulomb explosion of 1,2-diiodoethane I + images anti gauche 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 (S N 2: 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.  x-ray diffraction with free-electron laser sources Calculations by Henry Chapman OUTLOOK

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

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

47. Enjoy the silence

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

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

52. Control of conformations !

53. Nonadiabatic alignment 670 fs alignment pulse on iodobenzene

55. Possible Experiments - FLASH: Photoelectron spectroscopy (angular distributions) - FLASH / LCLS / XFEL: Ionization dependence on alignment - LCLS / XFEL : x-ray diffraction

56. Practical Aspects  Repetition rate of alignment lasers versus FEL (FLASH, LCLS, XFEL)  Repetition rate of pulsed molecular valve  Choice of alignment laser (YAG, fs laser)  Alignment laser should have excellent spatial structure (focus)  Source of molecules: Cold molecular beam  Further control: Conformations