cmlap FEMTOCHEMISTRY Experimental observation and control of molecular

címlap FEMTOCHEMISTRY Experimental observation and control of molecular dynamics

időskála 2 CPU clock cycle time atomic nucleus - neutrino interaction nuclear motion in atomic nuclei yocto- zepto- femto- pico- second 10 -3 10 -6 10 -9 10 -12 10 -15 10 -18 10 -21 10 -24 micro- 1 milli- 103 electronand energytransfer molecular vibration molecular rotation nano- one minut 106 kilo- length of a day 1012 109 giga- 1015 mega- lifetime of the triplet excited state tera- human lifespan lifetime of the singulet excited state atto- appearance of humans vibrational relaxation solvation peta- the age of Earth Time window of elementary reactions molecule - photon interaction What is „femtochemistry” ?

időskála 3 molecular vibration molecular rotation lasermode amplified laser mixing; flow; flash + pulse compression photolysis locking stopwatch distance photolysis delay time oscilloscope delay time control optical path yocto- zepto- femto- pico- nano- 10 -3 10 -6 10 -9 10 -12 10 -15 10 -18 10 -21 10 -24 mikro- 1 electronand energytransfer nuclear motion in atomic nuclei lifetime of the triplet excited state milli- 103 kilo- one minut 106 mega- length of a day 1012 109 tera- human lifespan 1015 giga- lifetime of the singulet excited state atto- appearance of humans solvation peta- the age of Earth vibrational relaxation molecule - photon interaction 1949 -1967 -1972 -1985 18501900 -1900 -1949 atomic nucleus - neutrino interaction Time window of kinetic measurements

időfelbontás increase in time resolution 1011 times increase within 36 years!! time, seconds amplified lasers + pulse compression delay time picosecond lasers (ring lasers) oscilloscope, delay nanosecond lasers (mode locking) oscilloscope, delay flash photolysis + relaxation optical path length + oscilloscope flow methods distance control year

Zewail Ahmed Zewail, 1999 Nobel-prize in chemistry Born 1946 in Egypt B. Sc. at Alexandria University (Egypt), then University of Pennsylvania (U. S. A. ) Ph. D. 1974– 76 University of California Berkely 1976– California Institute of Technology 1990– professor, head of the Chemical Physics Division Wolf-prize (1993), Nobel-prize (1999) Professor & Doctor honoris causa (ELTE, 2009) Nobel-prize for experimental studies at femtosecond timescale in transition-state spectroscopy

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

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

Na. D szárnyak Experimental observation of the transition state F + Na 2 [F····Na ]‡ Na. F + Na*

Na. D szárnyak 2 Experimental observation of the transition state F + Na 2 wing [F····Na ]‡ Na. F + Na* Na-D line intensity: 1 „wings” intensity: 0. 000001. . . 0. 000002 D-line wing REASON: FNa 2‡ lifetime is approximately 10 – 13 s detection time: 10 – 7 s, random formation of transition state molecules

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

pump-probe Spectroscopy with femtosecond time resolution: experimental arrangement reference detector Nd: YAG laser probe sample Ar- ion laser excitation H 2 O amplifier delay (1 fs = 0. 3 CPM laser m path length) Laser technics: http: //femto. chem. elte. hu/kinetika/Laser. htm

pump-probe 1 Spectroscopy with femtosecond time resolution: experimental equipment Femtochemistry laboratory Sherbrooke University, Canada 1988 1 m Laser technics: http: //femto. chem. elte. hu/kinetika/Laser. htm

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

pump-probe 3 Spectroscopy with femtosecond time resolution: experimental equipment Faraday isolator delay line BBO optical fibre Ti-sapphire laser chopper dicroic mirror monochromator sample parabolic mirror

pump-probe 4 Spectroscopy with femtosecond time resolution: experimental equipment 10 cm Femtochemistry laboratory, MTA SZFKI, 2002 Hungary

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

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

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

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

pump-probe 5 Spectroscopy with femtosecond time resolution: background of the experiment potential energy ultrashort pulse coherence and selectivity 1 fs = 0. 3 m path length reaction coordinate time

koherencia incoherent movement

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

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

lassított felvétel Spectroscopy with femtosecond time resolution: construction of slow motion pictures 1 fs = 0. 3 m path length reference detector Nd: YAG laser probe sample Ar- ion laser excitation amplifier CPM laser delay line 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 pulse is released only after 0. 1 -0. 01 seconds

lassított felvétel 2 Analogy: slow motion video of 100 metres sprint race „femtosecond-like” technics of slow motion 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 pulse is released only after 0. 1 -0. 01 seconds

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

Direct experimental measurement of PES classical mechanics approach klasszikus Bersohn, R. , Zewail, A. H. : Ber. Bunsenges. Phys. Chem. 92, 373 (1988) potential interatomic distance reaction time

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

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

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

ciklobután Reaction types, PES surfaces, ultrafast kinetics: decomposition of cyclo butene 2 ethenes observed

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

Reaction types, PES surfaces, ultrafast kinetics: bimolecular reactions bimolekulás 1 IH · CO 2 van der Waals complex flying in the molecular beam due to the exciting pulse, the IH molecule dissociates → the H-atom is projected onto the CO 2 molecule the exciting (”clocking”) pulse initiates a bimolecular reaction

Reaction types, PES surfaces, ultrafast kinetics: bimolecular reactions bimolekulás 2 formation of an H · · · CO 2 transition state products of the reaction: OH radical and CO molecule get away from each other the bimolecular reaction happens in a coherent way

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

kontroll Coherent control of chemical reactions: 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 production might lead to unprecedented perspectives in green chemistry.

kontroll 2 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) 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 state of the molecule, two pulses of different frequency can excite each of them. By varying the amplitude and phase between the two pulses, (the spectral and temporal distribution of the pulse sequence), the outcome can be controlled. Multiphoton CC: in case of two states having only slightly different energies, two pulses 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 outcome of the reaction can be controlled.

Fourier Another possibility: Controlling the chirp of spectrally broadened pulses Be f (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: If f is differentiable and , then (Heisenberg) uncertainty principle:

vibrációs fókusz Another possibility: Controlling the chirp of spectrally broadened pulses “vibrational focusing” of the exciting pulse on the anharmonic PES example: selective excitation of the vibrational mode of the I 2 molecule Krause, J. L. et al. : in: Femtosecond Chemistry, editors: Manz, J. , Wöste, L. , p. 743 -777, VCH, Weinheim (1995) optimális lokalizáció

centrifuga An interesting control type: the optical centrifuge Villeneuve, D. M. , et al. : Phys. Rev. Letters 85, 542 (2000) Control of the chirp of two circularly polarized, spectrally broadened pulses the absorbing molecule feels the resultant rotating field strength.

centrifuga 2 optical centrifuge Cl 2 isotope separation

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

elektron Electron solvation in polar solvents water methanol

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

metanolban Electron solvation in methanol Keszei et al. JCP 99, 2004 (1993) 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