1、Femtosecond Time-Resolved Photoelectron SpectroscopyOutlineIntroduction of femtosecond TRPESExperimental methods of TRPESDevelopment of TRPESApplications of femtosecond TRPESFuture directions Why do we research femtosecond chemistry?Chemical bonds form and break on the femtosecond time scale,and on
2、this time scale of time we can freeze the transition states at configurations never seen before.Even if there is no reactants-to-products transformation-physical change-one is observing the most elementary of all molecular process.IntroductionA.H.Zewail was awarded the Nobel prize in chemistry in 19
3、99.“Femtochemistry has fundamentally changed our view of chemical reac-tions.”Zewail,A.H.J.Phys.Chem.A 2000,104,5660 Zewail,A.H.et al,Nature 1992,355,66.Why do we research femtosecond TRPES?laser-induced fluorescence resonant multiphoton ionizationa small region of the reaction coordinateresonant wi
4、th an electronic transition how?photoelectron spectroscopy1.1 General aspects of femtosecond TRPESThe pump pulse is over,the wave packet (t),given by eq 1,Si(t)=f(r).EPROBE(t)2=nbne-i2cEnt2(2)Si(t)=nmnbnbmcos(En-Em)2ct+nmnan(t)=ne-i2cEnt(1)bnan=f(r).EPROBE(t)nwhere,1.2 Photoelectron angular distribu
5、tion(PADs)Within the molecular frame,the symmetries of the outgo-ing electron partial waves are likewise related to the sym-metry of the electronic state undergoing ionization.Thiscan be written as:ex +e-TSex:the symmetry species of the prepared excited state:the dipole operator+:the ion statee-:the
6、 symmetry species of the outgoing electronTS:the totally symmetric species2.1 How to complete femtosecond TRPES?femtosecond pump-probe pulse!Experiment2.2 Schematic of femtosecond laserCompressorStrecherTi:Sapphire oscillatorAr+laserRegernerative amplifierNd:YAG laser20 W,3.0 kHz532 nm 800 nm,1520 f
7、s250 mW at 86 MHz30 nJ/pulseFinal Output:800 nm,6080 fs500 mW,at 3.0 kHz200 J/pulseDouble frequency:400 nm,100 fs130 mW,at 3.0 kHz40 J/pulseBBO200 ps2.5 W5.0 W2.3 the detector of Photoelectron spectroscopyMagnetic bottle time-of-flight spectrometerAdv.:high collection efficiency simple,rapid data re
8、adout straightforward photoelectron-photoion coincidence meas-urements(PEPICO)Disadv.:no angular distributions low resolution2D photoelectron imaging techniques(velocity-map imaging)Adv.:electron kinetic energy distributions angular distributionsDisadv.:image reconstruction coincident pump and probe
9、 laser reference frames 3D imaging techniques!2.4 Photoelectron-photoion coincidence methods“Magic bottle”electron spectrometer:photoelectron time-of-flightCollinear time-of-flight mass spectrometer:the mass of parent ionTime-resolved PEPICO:photoelectron and photoion kinetic energy distributionAngl
10、e-resolved PEPICO:photoelectron and photoion angular distributionStert,V.;Radloff,W.;et al,Europhys.Lett.1997,40,515.Garner,M.C.,Hanold,K.A.;et al,J.Phys.Chem.A 1997,101,6577.3.Development of TRPES ns and ps TRPES:gas-phase ps TRPES:intramolcular vibration relaxation ps TRPES:reaction and solvation
11、dynamics within clusters fs TRPES:non-adiabatic dynamics of polyatomic molecules anion photodissociation and wave packet dynamics metal cluster anions and neutral clusters dynamics photodissociation dynamics of polyatomic molecules photoelectron-photoion coincidence detection technique photoelectron
12、 angular distributionsDevelopment4.1 Non-adiabatic intramolecular dynamicsBlanchet,V.;Zgierski,M.Z.J.Chem.Phys.2001,114,1194.Application4.2 Photodissociation dynamics of NO2 Davies,J.A.;Leclaire,J.E;Continetti,R.E.J.Chem.Phy.1999,111,1.Davies,J.A.;Continetti,R.E.;Chandler,D.W.Phys.Rev.Lett.2000,84,5
13、983.4.3 Electron solvation in finite systems:femtosecond dynamics of iodide(water)n anion clustersLehr,L.;Zanni,M.T.;Frischkorn,C.,Science,1999,284,635.Development in detector technologiesDevelopment of multiply photoelectron-photofr-agment coincidence and coincidence-imaging methodsDevlopment of hi
14、gh average power femtosecond VUV/XUV source and the attosecond laser sourceFuture directions4.Applications of femtosecond TRPES Non-adiabatic intramolecular dynamicsExited-state intramolecular proton transferNeutrals photodissociation dynamics and reaction dynamicsAnion photodissociation dynamics and reaction dynamicsAnion intramolecular electronic relaxation dynamicsCharge-transfer-to-solvent and solvated electron dynamics
