Molecular Dynamics Studied by Picosecond X-ray Diffraction

Size: px

Start display at page:

Download "Molecular Dynamics Studied by Picosecond X-ray Diffraction"

Brett Horton
5 years ago
Views:

$Paris 17-3-25 Molecular Dynamics Studied by Picosecond X-ray Diffraction Experiments: Theory: Maciej Lorenc,$

1 Paris Molecular Dynamics Studied by Picosecond X-ray Diffraction Experiments: Theory: Maciej Lorenc, Qingyu Kong, Manuela Lo Russo, Marco Cammarata, Michael Wulff Savo Bratos, Rodolphe Vuilleumier, Fabien Mirloup,

2 The two-step dissociation of iodine from C 2 H 4 2 in methanol(hee et al.) C 2 H hv C 2 H 4 2 * C 2 H 4 + C 2 H Would like to know : Atomic composition and structure of intermediates Their life times and decay mechanism The interactions with the solvent(cage and bulk) solvation cage C H C H C H C H C H C H C H C H nitial state t< Bridged state ~1 ps Abstraction ~4 ns End state t > 1 ns

$Time resolved diffraction experiments: optical$ ) chopper( 986.

3 Time resolved diffraction experiments: optical pump & x-ray probe laminar jet laser pulse(15 fs ) chopper( Hz) δt CCD detector (integrating) v x-ray pulse(1 ps) total signal difference signal

4 2.E+7 Energy: Spectrum from the mono-harmonic undulator U17 Flux: E f = 19. kev p = 1.1 x 1 9 ph/pulse(1ma) E com = kev = 1.1 x 1 12 ph/s(1ma) spectral flux: ph/.1%/pulse(1ma) 1.5E+7 1.E+7 E/E = 3.% 5.E+6 Focus Pulse length: τ= 6-12 ps(fwhm).e+ 1um 6um Pulse frequency: f = Hz energy(kev)

$tion) Diffracted ntensity S(q, t) Detector 12 q=k f -k i r k f ( 2Z ) 2 S(q) (e.u.$

5 Gas-phase(Debye Equation) Diffracted ntensity S(q, t) Detector 12 q=k f -k i r k f ( 2Z ) 2 S(q) (e.u.) S( q) = i, j f ( q) i f j sin( q r ( q) q r i, j i, j ) k i =2π/λ 2 Liquid-phase(Zernike-Prinz Equation) Positions given by atom-atom pair distributions g αβ (r) q(å -1 ) 15 S(q) ((e.u.) 2 /CCl Nα N β sin( q r) S( q, t) = f α ( q) f β ( q) Nαδαβ + gαβ ( r, t) 4π r αβ V q r 2 dr q(å -1 )

6 Molecular Dynamics Simulation of static g αβ (r) functions in CCl 4 (1:5) g αβ (r) Cl - Cl - Cl Cl r (A) We would like to measure the change in: 1) The solute structure( 2 ) 2) The cage structure( 2..Cl) 3) The bulk solvent structure(ccl 4 )

7 Potential energy curves for 2 3 B Energy[eV] 2 1 hν A/A' 1 π u β(27 ps) α(14ps) γ(22 ns) nteratomic distance [Å]

8 The time to reach thermal equilibrium in a 2 : CCl 4 solution(1: 675) < dist( 2 *, 2 *) > = 5 Å 2 wavefront(5%) l = χ t ; χ = κ ρ C p Temperature locally uniform in ~ 1 ps Energy dissipates out of x-ray volume in ~ 1 ms

9 Data collection with the CCD camera CCD-frame Triplet pictures: diff(n) = on(n) - ½ (off(n-1) + off(n)) laser: off on off on off on off on off on off on Delay: laser - xray - 1 ps -5 ps. ps 5 ps 1 ps 25 ps 1. ns 2.5 ns

10 Radial diffraction patterns from 2 in CCl 4 (1: 5) taken 1 ps after excitation. Exposure time : 5 s/image CCl CCD-counts/pixel ( ADU/5sec/ 1 ma) CCD-counts/pixel ( ADU/5sec/ 1 ma) Difference: laser on laser off Q = 4 π sin(θ )/ λ (Å -1 )

11 The difference oscillations from 2 * + CCl 4 * 1 ps after excitation PRL, vol 92, no 12, p , 24 2 * without interference with CCl 4 S(q)/ (e.u.) 2 /CCl 4 -molecule Occupancy Lifetime(ns) α: 66%.18 β: 2% 2.7 γ: 14% q(å -1 )

12 Watching atoms move: the real-space transform of S(q, τ) S[ r, τ ] 1 dq q S( q, τ )sin( qr) 2 2π r S[r, t] is a measure, biased by atomic formfactor, of the change in the radial-electron-density of an average excited atom

13 Radial maps of the recombination of Br 2 and 2 in CCl 4 after 1 ps Br 2 Formation of Br 2 *(A-state) τ = 1 ps δt = 2.3 K δp= 35 bar Delta S[ r ] [a.u.] Br 2 -hole 2 small molecule? Cl..Cl(1) Cl..Cl(2) Cl Cl hole -.15 Solute +(Solvent) Solvent only r(å)

14 The measured x-ray structure of liquid CCl 4 (E= 88 kev) 1.2 ntra molecular Cl-Cl 1 8 nter molecular 1 Cl Cl S Electron density(e/å 3 ).8.6 C-Cl Cl..Cl (1) Cl..Cl (2) Q(Å -1 ) x 1.4 First coordination shell second solvation shell third solvation shell r(å)

15 Visualising atomic motion by X-ray diffraction: probing atom-atom pair correlations g ab (r, t) though the Bratos Equation: = = β α αβ αβ β α β α τ τ τ π τ 1] ), ( [ ) ( 1 ) sin( ), ( ) ( ) ( 2 1 ], [ 1 2 r g w V const qr q qs q f q f dq r r S Chemical Physics 34, , (24) n the sub-molecular range: ( < r < 2 Å) : g αβ (r, τ) = => S[r, τ] probes the inverse volume of the solvent. C 2 H 4 2 in methanol M M V V density the change in the bulk probes V V r S ρ ρ τ τ = ) ( 1 1 ], [

16 The delayed thermal expansion of the solvent( 2 in CCl 4 ) Liquid jet Acoustic horizon: τ a = R / v s d~3 må laser 2R Longaker & Litvak: α P dq( t) ρ'( τ ) = dt( )[ 1+ exp( c C P ρ dt τ 2 ( τ t) 2 / R 2 ))]

17 delay 1 ps S(q,τ ) [ (e.u.) 2 / 2 -molecule] delay 1 ns iodine contribution full model delay 1 µs q=4π sin(θ)/λ [Å -1 ]

18 Dissociation energy levels of C 2 H 4 2 in methanol TS Relative energy /kcal mol bridge C 2 H 4 +2 TS C 2 H hv=4.647ev Linear-isomer -4

19 Calculating the q- and r-space signatures for a transition C 2 H hv(267nm) C 2 H 4 + C H C H C H C H

20 Difference oscillations from the transient state of C 2 H 4 2 *.25 Time delay: 1 ps, exposure time: 1s/CCD-frame.2.15 run1 run2 run3 run4 run5 average.1 q S(q) (a.u.) q = 4π sin(θ)/λ (Å -1 )

21 Radial map of C 2 H 4 2 * in methanol(ch 3 OH) at 1 ps 8.E-4 6.E-4 4.E-4 Cage + Solvent( T) run1 run2 run3 run4 run5 run6 2.E-4 average S[ r ] (a.u.).e+ -2.E-4-4.E-4-6.E-4 C- hole C H C H -8.E-4-1.E-3 - hole r(å)

23 ntermediates in the decay of C 2 H hν(267nm).. C 2 H C 2 H 4 2 C 2 H 4 2 C 2 H 4 Lifetimes: C 2 H 4 : 3.8 ns (uni-molecular) C 2 H 4 - : 1.4 ns (uni-molecular) C 2 H 4 -

24 The C 2 H 4 2 model: combination of uni and bimolecular reactions incl hydrodynamics of CH 3 OH. Unimolecular: C 2 H 4 2 C 2 H 4 + C 2 H 4 2 C 2 H C 2 H 4 C 2 H 4 + C 2 H 4 - C 2 H Bimolecular: C 2 H 4 + C 2 H δs (e.u.)/ch 3 OH τ = 1 ps, T=1.15 K, P=16.3 atm Q(Å -1 ) Q(Å -1 ) δs (e.u.)/ch 3 OH δs (e.u.)/ch 3 OH δs (e.u.)/ch 3 OH τ = 1 ns, T=1.28 K, P=17.9 atm τ = 1 ns, T=1.3 K, P=18. atm τ = 1 ns, T=1.15 K, P=16.3 atm Q(Å -1 ) Q(Å -1 )

25 Multilayer optics(cryogenically cooled) ( Ru / B 4 C ) 51 : d = 39.2 Å, 1-2 kev, δe/e = 3.1% ( r / Al 2 O 3 ) 1 : d = Å, 2-3 kev, δe/e = 1.9% sin A B

26 The effect of the asymmetric undulator spectrum Leads to: phase shift and damping of oscillations Solution: multilayer optics 2.E+7 Spectrum of U17 undulator spectral flux: ph/.1%/pulse(1ma) 1.5E+7 1.E+7 5.E+6.E energy(kev)

$Ultrafast Electron Diffraction(UED), Zewail, Caltech.$

27 Ultrafast Electron Diffraction(UED), Zewail, Caltech. UED (gas phase) UXD(ESRF) (condensed phase) XFEL (condensed phase) Relative scattering power Electron or photon flux /pulse 1 x 1 9 / pulse 1 x 1 12 / pulse Repetition rate 1 Hz 1 Hz 1 Hz Number of solute molecules x x 1 13 Overall signal from solutes Background from solvent none huge huge Pulse width 1 ps 1 ps 1 fs

28 Acknowledgments1 Friedrich Schotte(D) Marco Cammarata() Qinyu Kong( C) Maciej Lorenc(PL)

29 Acknowledgments2 Fabien Mirloup Rodolphe Vuilleumier Technical support: Laurent Eybert Laurent Claustre Wolfgang Reichenbach ESRF staff and management Friedrich Schotte(D) Harry hee(korea) Philip Anfinrud(NH, Bethesda, USA ) Friedrich Schotte(D) Anton Plech(Konstanz) Savo Bratos(Paris) Manuela Lo Russo(ESRF)

Impulsive solvent heating probed by picosecond x-ray diffraction

$Impulsive solvent heating probed by picosecond x-ray diffraction$ THE JOURNAL OF CHEMICAL PHYSICS 124, 124504 2006 Impulsive solvent heating probed by picosecond x-ray diffraction M. Cammarata European Synchrotron Radiation Facility, BP 220, Grenoble Cedex 38043, France;