1. Making molecules sing: Quantum beats and interference as probes of molecular structure Katharine Reid Inaugural lecture, May 27 th 2010

2. Wolverley High School, Kidderminster

3. Science at Wolverley Melvyn Kershaw

4. University of Sussex

5. Chemical Physics at Sussex Harry KrotoTony StaceTony McCafferyJohn Murrell

6. Light Sources

7. FlashlampLaser Broad band Incoherent Pulsed Narrow band Coherent Continuous

8. Spectral profile and bandwidth FlashlampContinuous laser

9. Molecules in excited states

10. Laser induced fluorescence

12. State-selection and detection

13. excitationcollisionemission Probing the dynamics of chemical reactions

14. Dick Zare

15. Stanford University

16. Interference Thomas Young A double slit

17. Interference Constructive: bright spot

18. Interference Destructive: dark spot

19. d L y Interference The first bright spot occurs at y = L/d If = 530 nm (green), L = 14 m and d = 50 microns Maximum of first bright spot is at y = 14.8 cm

20. Electron waves Atomic orbitals – bound electrons

21. Ejecting electrons with light

22. Simplifying spectra Thermal congestion State selection

23. Photoelectron interference patterns Laser polarization direction Constructive interference Destructive interference These patterns provide unique information on molecular structure

25. University of Nottingham Lunch time near the School of Chemistry, University Park!!

26. The “younger chemists” c. 1996

27. Who is the odd one out?

28. Time-resolved measurements

29. Photoinitiation of H 2 + Cl 2

30. Flash photolysis The Nobel Prize in Chemistry 1967 EigenNorrishPorter "for their studies of extremely fast chemical reactions, effected by disturbing the equilibrium by means of very short pulses of energy"

31. Understanding photochemistry visionphotosynthesissolar cells

32. Laser Bandwidth narrow band continuous/long pulse broad band short pulse

33. State-selection... Narrow band Long pulse Broad band Short pulse

34. Vibrational states in polyatomic molecules

35. On excitation only certain vibrational states can be prepared

36. Vibrations can be coupled

37. Time-resolved measurements t = 0 t1t1 t2t2

38. Nano what? 1 ps = 1000 fs

39. Femtochemistry The Nobel Prize in Chemistry 1999 "for his studies of the transition states of chemical reactions using femtosecond spectroscopy” Ahmed Zewail

40. Intramolecular vibrational energy redistribution Timescale: tens of picoseconds

41. Questions 1.What is the timescale? 2.What is the mechanism (which dark states are involved)? 3.Can we influence the process? (Bond-selective chemistry, coherent control, mode-specificity) 4.What can we learn about chemical reactivity?

42. The experiments!

43. Toluene absorption spectrum

44. Photoelectron imaging

45. t = 0 t1t1 t2t2

46. 0 ps

47. 1 ps

48. 2 ps

49. 3 ps

50. 4 ps

51. 5 ps

52. 6 ps

53. Time-resolved photoelectron spectra

54. Peak intensities versus time Time delay / picoseconds

55. Quantum beats

56. Beating patterns E 4 329.63 Hz F 4 349.23 Hz

57. Making molecules sing?

58. Coupled vibrational states Three states = two observable frequencies

59. Analysis of quantum beats in toluene From this we can learn: 1.The timescale of the dynamics 2.The “coupling matrix elements” 3.The exact vibrational energies More importantly, we have developed and tested a method that can be used to interrogate more complicated dynamical processes.

60. Toluene at higher excitation energy... Intensity decreases with time Intensity increases with time

61. Where to from here?

63. Support Neil Barnes Mike Towrie Pavel Matousek Kate Ronayne The workshop Students Dave Townsend Paul Whiteside Chris Hammond Paul Hockett Mick Staniforth Alistair Green Jonathan Midgley Postdocs Simon Duxon Tom Field Jon Underwood Julia Davies Susan Bellm Adrian King Help with this lecture Neil Barnes Paul Gaetto Collaborators Ivan Powis Tim Wright Thanks to: Mentors Melvyn Kershaw Tony McCaffery Dick Zare

64. And thanks to everyone for their support.