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
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
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
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)
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
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
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)
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
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
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)
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
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
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
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
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
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