Femtochemistry: Observing and Controlling Molecular Dynamics

1. címlap FEMTOCHEMISTRY Experimental observation and controlof molecular dynamics

2. Timewindow of elementary reactions vibrationalrelaxation solvation electron-andenergy-transfer atomic nucleus - neutrino interaction lifetimeof thesinguletexcited state nuclear motion in atomic nuclei molecule - photon interaction length of a day human lifespan lifetimeof thetripletexcited state molecularvibration one minut molecularrotation 1015 1012 109 106 103 1 10-3 10-6 10-9 10-12 10-15 10-18 10-21 10-24 atto- milli- pico- nano- kilo- peta- giga- tera- yocto- micro- zepto- mega- femto- CPU clock cycle time What is „femtochemistry” ? időskála 2 appearance of humans the age of Earth second

3. 1985- 1850-1900 1900-1949 1949-1967 1967-1972 1972-1985 vibrationalrelaxation solvation electron-andenergy-transfer atomic nucleus - neutrino interaction lifetimeof thesinguletexcited state nuclear motion in atomic nuclei molecule - photon interaction appearance of humans length of a day human lifespan the age of Earth lifetimeof thetripletexcited state molecularvibration one minut molecularrotation 1015 1012 109 106 103 1 10-3 10-6 10-9 10-12 10-15 10-18 10-21 10-24 atto- kilo- milli- pico- peta- giga- tera- yocto- zepto- mikro- nano- femto- mega- amplified laser+ pulse compression delay time mixing; stopwatch modelockingdelay time flash photolysisoptical path flow;distancecontrol laser- photolysisoscilloscope Time window of kinetic measurements időskála 3

4. increase in time resolution időfelbontás 1011 times increase within 36 years!! amplified lasers+ pulse compressiondelay time time, seconds picosecond lasers (ring lasers)oscilloscope, delay nanosecond lasers (mode locking)oscilloscope, delay flash photolysis + relaxationoptical path length + oscilloscope flow methodsdistance control year

5. Ahmed Zewail, 1999 Nobel-prize in chemistry Zewail Born 1946 in EgyptB. Sc. at Alexandria University (Egypt), then University of Pennsylvania (U.S.A.) Ph. D. 1974 1974–76 University of California Berkely1976– California Institute of Technology1990– professor, head of the Chemical Physics DivisionWolf-prize (1993), Nobel-prize (1999)Professor & Doctor honoris causa (ELTE, 2009) Nobel-prize for experimental studies at femtosecond timescale in transition-state spectroscopy

6. Some history: dynamics of chemical reactions történelem Pfaundler:collision theory + Maxwell-Boltzmann distributionin interpreting chemical reactions. Reaction can occur onlyif reactants have larger energy than needed to pass threshold. 1867 Marcelin: applying Lagrange-Hamilton (mechanical)formalism and Gibbs-type statistical thermodynamicsN atomsin a 2N dimensional phase space 1914 Eyring and Polányi: transition state theory(absolute rate theory, transition complex theory)N atoms’ trajectory on a stationary potential energy surface 1935

7. F + Na2 [F····Na····Na ]‡ NaF + Na* Experimental observation of the transition state történelem 2 1986 John Polanyi, sharing the chemistry Nobel-prize

8. F + Na2 [F····Na····Na ]‡ NaF + Na* Experimental observation of the transition state NaD szárnyak

9. F + Na2 [F····Na····Na ]‡ NaF + Na* wing wing Experimental observation of the transition state NaD szárnyak 2 Na-D line intensity: 1„wings” intensity: 0.000001 .....0.000002 D-line  REASON: FNa2‡ lifetime is approximately 10–13 sdetection time: 10–7 s, random formation of transition state molecules

10. A–B–C A + BC Introduction: basics of laser photolysis lézerfotolízis Potential energy higher excited state excited state ground state A – BC distance

11. reference detector Nd:YAGlaser probe sample Ar- ionlaser excitation H2O CPMlaser amplifier delay Spectroscopy with femtosecond time resolution:experimental arrangement pump-probe (1 fs = 0.3 m path length) Laser technics: http://femto.chem.elte.hu/kinetika/Laser/Laser.htm

12. Spectroscopy with femtosecond time resolution:experimental equipment pump-probe 1 Femtochemistry laboratory Sherbrooke University, Canada1988 1 m Laser technics: http://femto.chem.elte.hu/kinetika/Laser/Laser.htm

13. prism Ar-ion laser slit Ti-sapphire crystal prism birefrigent filter Spectroscopy with femtosecond time resolution:experimental equipment pump-probe 2 Laser technics: http://femto.chem.elte.hu/kinetika/Laser/Laser.htm

14. Faraday isolator delay line monochromator BBO sample dicroic mirror optical fibre parabolic mirror chopper Ti-sapphire laser Spectroscopy with femtosecond time resolution:experimental equipment pump-probe3

15. Spectroscopy with femtosecond time resolution:experimental equipment pump-probe4 10cm Femtochemistry laboratory, MTA SZFKI,2002 Hungary

16. probe excitation intensity delay time time Spectroscopy with femtosecond time resolution:delay line Késleltetés 1

17. probe excitation intensity delay time time Spectroscopy with femtosecond time resolution:delay line Késleltetés 2

18. probe excitation delay time Spectroscopy with femtosecond time resolution:delay line Késleltetés 3 intensity time

19. probe excitation delay time Spectroscopy with femtosecond time resolution:delay line Késleltetés 4 intensity time

20. Spectroscopy with femtosecond time resolution:background of the experiment pump-probe 5 ultrashort pulse  coherence and selectivity 1 fs = 0.3 m pathlength potential energy reaction coordinate time

21. koherencia incoherent movement coherentmovement

22. Spectroscopy with femtosecond time resolution:experimental results pump-probe 6 LIF signal potential energy reaction coordinate delay time, fs

23. Spectroscopy with femtosecond time resolution:experimental results konvolúció the laser pulse broadens– temporally– spectrally LIF signal delay time, fs time OCR = optically coupled region

24. reference detector Nd:YAGlaser probe sample Ar- ionlaser excitation CPMlaser amplifier delay line Spectroscopy with femtosecond time resolution:construction of slow motion pictures lassított felvétel 1 fs = 0.3 m pathlength time 1.an excitation pulse is released towards the sample 2.the excitation pulse is followed after some delay by a probe pulse 3.the detector measures the (integrated) laser-induced fluorescence 4.the next excitation pulseis released only after 0.1-0.01 seconds

25. 1.the race starts following the starter pistol’s signal 2.following the start, runners arrive to the fixed position of the camera 3.the camera is registering one single picture 4.the next race will start only after 300 thousand years 1.an excitation pulse is released towards the sample 2.the excitation pulse is followed after some delay by a probe pulse 3.the detector measures the (integrated) laser-induced fluorescence 4.the next excitation pulseis released only after 0.1-0.01 seconds Analogy: slow motion video of 100 metres sprint race„femtosecond-like” technics of slow motion lassított felvétel 2

26. ICN [I····CN ]‡ I + CN Reaction types, PES surfaces, ultrafast kinetics:dissociation of the ICN molecule I ··· CN LIF signal OCR potential energy reaction coordinate delay time, fs

27. Direct experimental measurement of PESclassical mechanics approachBersohn, R. , Zewail, A. H.: Ber. Bunsenges. Phys. Chem. 92, 373 (1988) klasszikus potential interatomic distance reaction time

28. Direct experimental measurement of PESquantum mechanical approachWilliams, S. O. , Imre, D. G.: J. Phys. Chem. 92, 6648 (1988) kvantum 0 time (fs) 20 wavefunction 40 60 80 100 140 180 potential of the excited state 0 8 10 4 C – I interatomic distance

29. Na+I– [Na····I ]‡ Na + I „avoided crossing” (degeneráció) covalent ionic Reaction types, PES surfaces, ultrafast kinetics:dissociation of the NaI molecule Na ··· I ionic LIF signal covalent NaI potential energy covalent free Na ionic delay time, fs interatomic distance, nm

30. Reaction types, PES surfaces, ultrafast kinetics:dissociation of the NaI molecule Na ··· I / 2 LIF signal delay time, fs

31. Reaction types, PES surfaces, ultrafast kinetics:decomposition of cyclobutene ciklobután cyclo butene  2 ethenes  observed

32. Reaction types, PES surfaces, ultrafast kinetics:bimolecular reactions molekulasugár Ahmed Zewail: Nobel lecture, December 8, 1999 Molecular beamand laser beam crossed in vacuum

33. IH·CO2van der Waals complex flying in the molecular beam Reaction types, PES surfaces, ultrafast kinetics:bimolecular reactions bimolekulás1 due to the exciting pulse, theIH molecule dissociates→ the H-atom is projected onto the CO2molecule the exciting(”clocking”) pulse initiates a bimolecular reaction

34. Reaction types, PES surfaces, ultrafast kinetics:bimolecular reactions bimolekulás2 formation of an H· · · CO2transition state products of the reaction:OH radical and COmoleculeget away from each other the bimolecular reaction happens in a coherent way

35. Reaction types, PES surfaces, ultrafast kinetics:bimolecular reactions bimolekulás IH·CO2 I + H·CO2 1st step: initiation of the reaction: H + OCO [H···O···C–O ]‡  HO + CO 2nd step : bimolecular reaction: Result: fluorescence of the OH radical appears after about 5 ps only [H···O···C – O ]‡ potential energy Potenciális energia HO + CO H + OCO HOCO valley reaction coordinate reakciókoordináta

36. Coherent control of chemical reactions: kontroll shaping the wave function of the transition state aka: quantum control Most (industrially important) reactions have different pathways (products) quantum control: with specific shaping of the transition state, it is possible to enable only the desired reaction path, i. e.to get only the desired product Technics: applying specifically shaped and timed pulses (temporal shape, polarisation, spectral distribution, delay)the shape of the transition state evolves differently, i. e.the reaction path changes, resulting in a different product If applied properly, by selecting the desired reaction pathways, clean, environmentally friendly, wasteless chemical productionmight lead to unprecedented perspectives in green chemistry.

37. Technical possibilities of coherent control Problem: when selectively exciting one specific bond, excitation energy is quickly distributed onto the other bonds as well (IVR = Internal Vibrational Relaxation; ~ 1 ps) kontroll 2 Solution: interferences between the different molecular modes should be influenced in a way that a constructive interference occures in the molecular mode leading to the desired reaction path We have to know interactions between the pulses and the molecules, as well as between the different modes of the molecules Technique: internal coherence of the molecules is achieved by properly applying the coherence of the external field in the form of the puls(es) Some possibilities: Frequency Resolved Coherent Control (CC): in case of two dissociative stateof the molecule, two pulses of different frequency can excite each of them. By varying the amplitude and phase between the two pulses, (the spectral andtemporal distribution of the pulse sequence), the outcome can be controlled. Multiphoton CC: in case of two states having only slightly different energies, twopulses can excite each of them, but with a different number of absorbed photons.Changing the ratio of the higher harmonic components of the pulses, the outcomeof the reaction can be controlled.

38. Another possibility: Controlling the chirp of spectrally broadened pulses Fourier Bef(t) and F() mutual Fourier-transformed in the time and frequency domains: Let us define their “widths” the following way: N is the second norm: , then If f is differentiable and (Heisenberg) uncertainty principle:

39. Another possibility: Controlling the chirp of spectrally broadened pulses “vibrational focusing” of the exciting pulse on the anharmonic PES vibrációs fókusz example: selective excitation of the vibrational mode of the I2 molecule Krause, J. L. et al.: in: Femtosecond Chemistry, editors: Manz, J., Wöste, L., p. 743-777, VCH, Weinheim (1995) optimális lokalizáció

40. An interesting control type: the optical centrifuge centrifuga Villeneuve, D. M. ,et al.: Phys. Rev. Letters85, 542 (2000) Control of the chirp of two circularly polarized, spectrally broadened pulsesthe absorbing molecule feels the resultant rotating field strength.

41. optical centrifuge centrifuga 2 Cl2 isotope separation

42. Further achievements ED, EC, EM Annu. Rev. Phys. Chem. 2006. 57 UED:ultrafast electron diffractiona photocathode is illuminated by the detecting laser pulse, electrons leaving the cathode are used to determine structure UEC:ultrafast electron crystallographysame as UED, but the electron beam is scattered not by moleculecules but crystals (e. g. phase transition) UEM:ultrafast electron microscopysimilar to UED, but instead of diffraction, ultrafast transmission electron microscopy UXD:ultrafast X-ray diffractionsimilar to UED, but ultrafast laser pulses produce X-ray pulses to determine molecular structure

43. Electron solvation in polar solvents elektron water methanol

44. Electron solvation in water elektron vízben E. Keszei, S. Nagy, T. H. Murphrey, P. J. Rossky, J. Chem. Phys. 99, 2004 (1993) diabatic quantum dynamical simulations in water: indirect solvation direct solvation E. Keszei, T. H. Murphrey, and P. J. Rossky, J. Phys. Chem., 99, 22 (1995)

45. Electron solvation in methanol Keszei et al. JCP 99, 2004 (1993) metanolban C. Pépin, T. Goulet, D. Houde,J.-P. Jay-Gerin, JPC 98, 7009 (1994) Keszei et al. JPC 101, 5469 (1997):either mechanisms can be fitted well