j. kohlbrecher, polarized solid targets, honnef 2003 dynamics of nuclear spin polarization j....
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![Page 1: J. Kohlbrecher, Polarized Solid Targets, Honnef 2003 Dynamics Of Nuclear Spin Polarization J. Kohlbrecher Paul Scherrer Institute CH-5232 Villigen Switzerland](https://reader034.vdocument.in/reader034/viewer/2022051417/5697c02a1a28abf838cd80a5/html5/thumbnails/1.jpg)
J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Dynamics Of Nuclear Spin Dynamics Of Nuclear Spin PolarizationPolarization
J. Kohlbrecher
Paul Scherrer InstituteCH-5232 Villigen
Switzerland
B. van den Brandt, P. Hautle, J. Kohlbrecher,
J.A. Konter, S. Mango (PSI)H. Glättli, E. Leymarie (CEA-Saclay)I. Grillo, R. May (ILL)H. Jouve, H.B. Stuhrmann (IBS)O. Zimmer (TU München)
investigated by simultaneous NMR investigated by simultaneous NMR and and
polarized neutron scatteringpolarized neutron scattering
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
DNP: a two step process
How to measure clusters of polarized protons
1. scattering of polarized neutron on polarized nuclei
2. small angle neutron scattering (SANS)
model system: EHBA-Cr(V)
time-resolved SANS and NMR experiments
Dynamics Of Nuclear Spin Dynamics Of Nuclear Spin PolarizationPolarizationinvestigated by simultaneous NMR investigated by simultaneous NMR
and polarized neutron scatteringand polarized neutron scattering
Contents:Contents:
Joachim Kohlbrecher
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
• protons close to electron polarize first
• time constant: ttpolpol < 1 s < 1 s
electron
1.1.
proton
polarization diffuses to the bulk protons by flip-flop transitions
time constant: tdiff » few seconds
2.2.H0
DNP: a two step processDNP: a two step process
close protons: ● strongly coupled to the p.c.
● weakly coupled to the bulk
● “poorly visible" by cw-NMR
bulk protons: ● weakly coupled to the p.c
● "visible" by cw-NMR
paramagnetic centre generates strong local field
• microwave induced direct interaction falls off like r6
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
How to measure How to measure clusters of polarized protonsclusters of polarized protons
requirements for experimental method:
1. sensitive on polarization of protons2. sensitive on length scale in nm-range
what do we want to see:
1. time-dependent polarization built-up of the proton spins around the radical
2. and in the bulk
experimental method:
1. cw-NMR (bulk protons)2. neutron scattering technique (close
protons)
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Neutron scattering techniquepolarized neutron scattering on polarized polarized neutron scattering on polarized
nucleinucleicold neutrons and their interaction with matter
2
21
b
E
VEn
kin
kinn
refraction indexinteraction potential for a single atom
)(2
)(2
jjN
bm
V rrr
» range of V(r)
scattering length
wavelength: 4 Å frequency: 1.2 THzenergy: 5meV wavevector:
1.55 1/Åvelocity: 980 m/s temperature: 58 K
b scattering lengthdensity
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
parallel
neutron
isotopes =
½I = ½
b = b0 + bnI.s
spin dependent scattering length
neutron
isotopes =
½I = -½
antiparallel
Polarized neutron scattering Polarized neutron scattering on polarized nucleion polarized nuclei
proton:
b0 = -0.374 bn = 5.8254
- 2 - 1 0 1 2
scattering length <b> / 10- 12cm
1H2H12C14N16O
Pp=-1
Pp=1
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
How to measure How to measure clusters of polarized protonsclusters of polarized protons
requirements for experimental method:
1.1. sensitive on polarization of protonssensitive on polarization of protons2. sensitive on length scale in nm-range
what do we want to see:
1. time-dependent polarization built-up of the proton spins around the radical
2. and in the bulk
experimental method:
1. cw-NMR (bulk protons)2. neutron scattering technique (close
protons)
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
sample
scatteredneutrons
detector
incidentneutrons,
d 2sin
42
Qd
λ ≈ 0.5 nm
d ≈ 10 nmθ ≈ 3 deg
Small Angle Neutron ScatteringSmall Angle Neutron Scattering
neutronguide
velocity selector(mechanical)
iris for beam collimation
sample
primary beam stop
2-dimensionalposition sensitive
detector
Qk
k
0
2
2
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Formfactor in Formfactor in SANSSANS
2
3
23
)(
)cos()sin(3
3
4,,
QR
QRQRQRRRQI
shapeheight
0 1 2 3 4 5 6 7 80.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0 R=0.45nm, b2=1
R=0.45nm, b2=1.2
R=0.5nm, b2=1
R=0.5nm, b2=0.53
I(Q
) /
a.u
.
Q / nm-1
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
-0.1
-0.05
0
0.05
0.1
-10 -5 0 5 10
radius [Å]
scatt
eri
ng
len
gth
den
sit
y
P=-1 P=0 P=1
P=1
P=0
P=-1
21312
321
3121 )()()()(),,( QRFRQRFRPQRFRAIRRQI soshsocinc
Shell of polarized protons:
-0.1
-0.05
0
0.05
0.1
-10 -5 0 5 10
radius [Å]
scatt
eri
ng
len
gth
den
sit
y
P=-1 P=0 P=1
P=1
P=0
P=-1
R1
R2
[CrVO7C4]-
[C2H5]4
glycerol-water (80% ….. 98% deuterated)
bulk protonelectron close proton
Model System:Model System: EHBA-Cr(V) EHBA-Cr(V)
close protons
sample E5 (solvent 98% D)sample E2 (solvent 88% D)
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Time resolved data Time resolved data acquisitionacquisition
switch to negative polarizationfrequency
negative dynamic nuclear polarization (DNP): 10 s
time resolved acquisition
• 200 spectra (in time framestime frames of 0.1 s length)
• several hundreds of 20 s long cycles are averaged
precise scattering intensity for each time frame
switch to positive polarizationfrequency
positive dynamic nuclear polarization (DNP): 10 s
time resolved acquisition
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 0.1 st = 0.1 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 0.9 st = 0.9 s
t [s]
0 10 20
PH
Observation of polarized proton Observation of polarized proton clustersclusters
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 3.4 st = 3.4 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 10 st = 10 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 10.1 st = 10.1 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 10.9 st = 10.9 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 13.4 st = 13.4 s
t [s]
0 10 20
PH
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
Inte
nsité
[U.A
]
q [ Å-1 ]
t = 20 st = 20 s
t [s]
0 10 20
PH
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Results
Experimental results: 200 spectra of neutron scattering
interpretation of the scattering curves
Fitting parameters : R1, R2, A, IInc and P
Conditions: • R1 and R2 are constant and time independent,
• Incoherent scattering independent of Q but dependent on time
• homogeneous polarization of the protons in the shell, dependent on time
R1 = 3.4 ÅR2 = 4.9 Å
P(t) IInc(t)
2
1312
321
3121 )()()()(),,( QRFRQRFRPQRFRAIRRQI soshsocinc
close protons
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
time dependent polarization gradient between the close and bulk protons
time dependence of polarization
close protons ~ exponential (SANS)
bulk protons ~ linear (NMR)
time [s]
0 5 10 15 20
pola
rizatio
n
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
close protons (fit)bulk protons (NMR)
exponential fit (1= 1.1 s, 2= 5.5 s)
close protonsclose protons versus
bulk protonsbulk protons
Europhys. Lett. 59 (2002) 62-67
characterization:sum of two exponential
t1 = 1.1s t2 =
5.5s
Time evolution of the polarization
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J. Kohlbrecher, Polarized Solid Targets, Honnef 2003
PAUL SCHERRER INSTITUT
Influence of the solvent deuteration
expected effect: faster diffusion of spin in solvent
Evolution of the close proton polarization for various solvent deuterations: 98%, 95% and 92% D
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.30.4
0.50.6
0.72
46
8101214161820I(
Q)
/ a.
u.
Q / A -1
time
/ se
c
EHBA, 95% deuterated solvent
0.45 0.50 0.55 0.60 0.65 0.70 0.75
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0.30.4
0.50.6
0.72468101214161820
I(Q
) /
a.u.
Q / A -1
tim
e /
sec
EHBA, 92% deuterated solvent1.3 1.4 1.5 1.6 1.7 1.8
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0.30.4
0.50.6
0.72
46
810
1214
161820I(
Q)
/ a.
u.
Q / A -1
time
/ se
c
EHBA, 98% deuterated solvent
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2