alignment, orientation and conformational control: applications in ultrafast imaging
DESCRIPTION
Alignment, orientation and conformational control: Applications in ultrafast imaging. Henrik Stapelfeldt. Department of Chemistry University of Aarhus Denmark. Ultra-fast Dynamic Imaging of Matter II April 30 – May 3, 2009. Purpose of this talk. - PowerPoint PPT PresentationTRANSCRIPT
Alignment, orientation and conformational control:
Applications in ultrafast imaging
Henrik Stapelfeldt
Department of ChemistryUniversity of Aarhus
Denmark
Ultra-fast Dynamic Imaging of Matter II
April 30 – May 3, 2009
Purpose of this talk
Recent progress in laser based alignment, orientation and conformer selection methods
List potential examples of ultrafast dynamic imaging
1-D Alignment
Order of the molecular geometry with respect to a space fixed axis
1-D Alignment
Order of the molecular geometry with respect to a space fixed axis
3-D Alignment
3-dimensional order of the molecular geometry
X
Y
Z
3-D Orientation1-D Orientation
Breaking the head for tail symmetry
How to align molecules
Use an intense (but not too intense) nonresonant pulse and rotationally cold molecules
a) Long pulse Adiabatic alignment
b) Short pulse Nonadiabatic alignment (transient / impulsive)
Classical picture of alignment
- Linear molecule
- Strong, linearly polarized laser field, E
Potential energy
)cos)((E
E periodopticalind
2204
121
E
High rotationalenergy
Low rotationalenergy
Quantum Mechanical picture of alignment
rotrotrotind2 E)E
21
JB(
Zon (1976), Friedrich + Herschbach (1995), Seideman (1995)
Solve the rotational Schrödinger equation
Pendular states : linear combination of field free rotational states
J
JMrot JMdMJ~For a linear molecule :
J = 2
J = 1
J = 0
Field-free states Pendular states
21
20
1000
11
3230 22
Adiabatic alignment slow turn-on of the alignment field
Alignment pulse = nanosecond pulse
Measurement of the spatialorientation of the molecules
m+
n+
Coulomb explosion :
light
I+
C6H3n+
lightF+
F+
Experimental Setup
CCD camera
25 fs ionization pulse
Mole
cular
bea
m
Supersonicexpansion
I+
I+
2-D ion detector
Alignment pulse
YAG : 9 ns 1064 nm
1D Alignment of iodobenzene (C6H5I)
I+ images
1D Alignment of Iodobenzene (C6H5I)
intensity and temperature dependence
1D Alignment of 4,4’ dibromobiphenyl (C12H8Br2)
Br+ images
3D alignment
Elliptically polarized long pulse
Larsen et al. PRL 2000 Tanji et al. PRA 2005
Perpendicularly-polarized pulse pair
Lee et al. PRL 2006 Viftrup et al. PRL 2007
Short elliptically polarized long pulse
Rouzée et al. PRA 2008
3D alignment - Elliptically polarized long pulse
End-viewI+
F+
2,6 dFIB
Rotational state selection of polar moleculesby electrostatic deflection
Strongly improved laser induced orientation and alignment
Setup and idea
Es
EYAG
Deflection of iodobenzene
0 kV
5 kV 10 kV
109 110 111 112 113 114
94 95 96 97 98 99
100 101 102 103 104 105
115 116 117 118 119 120
= 90 100 110 120 135 150
= 90 80 70 60 45 30
I+ -
C6H
5+
I+ -
C6H
52+EYAG
Estatic
EYAG
Estatic
= 90 100 110 120 135 150
= 90 80 70 60 45 30
Alignment and orientation of iodobenzene
EYAG
Estatic
EYAG
Estatic
Undeflected molecules
109 110 111 112 113 114
94 95 96 97 98 99
100 101 102 103 104 105
115 116 117 118 119 120
= 90 100 110 120 135 150
= 90 80 70 60 45 30
I+ -
C6H
5+
I+ -
C6H
52+EYAG
Estatic
EYAG
Estatic
= 90 100 110 120 135 150
= 90 80 70 60 45 30
Alignment and orientation of iodobenzene
EYAG
Estatic
EYAG
Estatic
Improved alignment
109 110 111 112 113 114
94 95 96 97 98 99
100 101 102 103 104 105
115 116 117 118 119 120
= 90 100 110 120 135 150
= 90 80 70 60 45 30
I+ -
C6H
5+
I+ -
C6H
52+EYAG
Estatic
EYAG
Estatic
= 90 100 110 120 135 150
= 90 80 70 60 45 30
Alignment and orientation of iodobenzene
EYAG
Estatic
EYAG
Estatic
Undeflected molecules
Orientation by mixed fieldsCombine static electric field and laser field
1>
2>
Static electric field mixes the pendular states:
”+” combination: 2> + 1> localization at = 0o
“-” combination: 2> - 1> localization at = 180o
1999:Friedrich + Herschbach
2001:Buck
2003:Sakai
θcosαI~ 20
Las
er i
nd
uce
d
p
ote
nti
al
BUT !
Different initial states orient in opposite directions
Averaging over the Boltzman distribution strongly diminishes the overall degree of orientation
Ideal target: All the molecules initially populated in the rotational ground state [or in the same rotational state (Marc Vrakking, Nat. Phys. 2009)]
Up-down asymmetryPhys. Rev. Lett. 102, 023001 (2009)
Deflection of iodobenzene seeded in He or in Ne
F. Filsinger et al., arXiv:0903.5413v1 (2009)
Up-down asymmetryF. Filsinger et al., arXiv:0903.5413v1 (2009)
Details of rotational quantum states
Latest improvements
capacitor plates
3D alignment - Elliptically polarized long pulse
Linear 1:4 1:2
2,6 dFIB
3D alignment - Elliptically polarized long pulse
Linear 1:4 1:2U
nd
eflectedD
eflected
2,6 dFIB
3D orientation
Undeflected DeflectedSee also:Sakai, PRA(2005)
Conformer selection
Cis and trans conformers of 3-aminophenol
cis-3AP trans-3AP
p = 2.3 D p = 0.7 D
Selective probing of cis and trans (REMPI)
S0
S1
Ip
Cis / trans confomer selection
Cis fraction
Side-view
Anti and gauche conformers of 1,2-diiodoethane(C2H4I2)
End-view
p = 0 D
anti gauche
p ~ 2 D
Deflection of 1,2-diiodoethane
11.0mm 10.1mm 9.7mmYAG
Cou
008 007 009
003 006 004+005
Coulomb explosion of 1,2-diiodoethane
I+ imagesanti gauche
Parallel fields
Perpendicular fields
CONCLUSIONS 1D and 3D aligned or oriented molecules are available for experiments
Adiabatic alignment provides strongest alignment and orientation BUT it is not field-free conditions
rapid truncation of alignment field [Stolow PRL (2003), Sakai PRL (2008)]
Quantum state selection can strongly enhance the degree of (adiabatic) alignment and orientation and alignment / orientation can be induced at lower fields!
Electrostatic beam deflection control of stereo isomers (conformers)
OUTLOOK Strong laser field phenomena - High harmonic generation - Electron diffraction
Selection of a single rotational quantum state (Marc Vrakking: NO and hexapole, Nat. Phys. March 2009)
Time resolved studies of chirality [PRL 102,/ 073007 (2009) ]
Steric effects in reactive scattering (SN2: Trippel and Wester)
Photoelectron angular distribution from fixed-in-space molecules [PRL 100, 093006 (2008) , Science 320, 1478 (2008) , Science 323, 1464 (2009)]
Aligned molecules as targets for free electron lasers
- FLASH: Photoelectron spectroscopy (angular distributions) - LCLS: x-ray diffraction
x-ray diffraction with free-electron laser sources
Calculations byHenry Chapman
OUTLOOK
X-ray diffraction from aligned molecules
Calculations by Henry Chapman
Planned target molecule
Deflection projectFritz Haber Institute, Berlin
Frank FilsingerJochen KüpperGerard Meijer
Lotte HolmegaardJens H. NielsenIftach NevoJonas L. Hansen
Enjoy the silence
X-ray beam
Molecular beam
Alignment beam
Beam overlap at LCLS !
X-ray beam
Molecular beam
Alignment beam
Beam overlap at LCLS !
Control of conformations !
Nonadiabatic alignment
0,440
0,490
0,540
0,590
0,640
0,690
0,740
0,790
0,00 5,00 10,00 15,00
0,44
0,49
0,54
0,59
0,64
0,69
0,74
0,79
335 340 345 350 355 360 365 370
0,44
0,49
0,54
0,59
0,64
0,69
0,74
0,79
690 695 700 705 710 715 720
0,44
0,49
0,54
0,59
0,64
0,69
0,74
0,79
335 340 345 350 355 360 365 370
0,44
0,49
0,54
0,59
0,64
0,69
0,74
0,79
690 695 700 705 710 715 720
0,44
0,49
0,54
0,59
0,64
0,69
0,74
0,79
0,00 5,00 10,00 15,00
Time (ps)
‹cos
2 θ›
No deflector Deflector 10kV
670 fs alignmentpulse oniodobenzene
Possible Experiments
- FLASH: Photoelectron spectroscopy (angular distributions)
- FLASH / LCLS / XFEL: Ionization dependence on alignment
- LCLS / XFEL : x-ray diffraction
Practical Aspects
Repetition rate of alignment lasers versus FEL (FLASH, LCLS, XFEL)
Repetition rate of pulsed molecular valve
Choice of alignment laser (YAG, fs laser)
Alignment laser should have excellent spatial structure (focus)
Source of molecules: Cold molecular beam
Further control: Conformations