Transcript UO4.ppt

The 61th International Symposium
on Molecular Spectroscopy, June 2006
The Permanent Electric Dipole Moment and
Magnetic g-factors of Uranium Monoxide, UO
Tongmei Ma and Timothy C. Steimle
Arizona State University, USA
Vasiliy Goncharov and Michael C. Heaven
Emory University, USA
Colan Linton
University of New Brunswick, Canada
Funded by: DoS_BES
Goals
1. Determine permanent electric dipole moments, m
2. Determine magnetic g-factors
3. Use results from “1” & “2” to test Ligand-field theory
LFT model successfully predicts properties of LnO & LnX(X=F,Cl,Br).
The validity of LFT to predict properties of actinides needs to be checked.

States with occupied s-orbitals have small values of m;
m(ns2) < m(ns1) <m(ns0)

States with high angular momentum have large magnetic gfactors.
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Related Spectroscopic and theoretical studies of UO
 Kaledin & Heaven, J. Mol. Spec. 1994



Visible LIF  33 bands (many bands rot. Analyzed).
Established =4 for the ground state: X(1)4.
“semi-empirical” LFT model low-lying state identification.
 Pitzer Group (Tyagi Ph.D. thesis): Relativistic ab initio predictions to
ground and low-lying excited states of UO.
U2+(5f37s)O2-& U2+(5f27s2)O2- configurations both important.
 Krauss & Stevens ab initio REP MCSCF (JCP 2003):
 Ground State m=3.86 D
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Experimental approach
UO skimmed mol. beam: Pulse Valve/Ablation Source
355 nm
Nd:YAG Pulse
Laser
Pulse Valve
Ar
Plasma
Depleted 238U Rod
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Near natural line width optical spectroscopy:
High-resolution LIF spectrometer
Optical Stark spectroscopy
Optical Zeeman Spectroscopy
600 nm (10)
Bandpass Filter
Stark
platesCoils
Helmholtz
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Electromagnet for Zeeman
spectroscopy (56G-1.2kG)
Mirror
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Results and Discussion
Two band systems
 [18403](=)5-X(1) (=)4, (0,0): P, Q, R
Stark:
// and  of R(4), 66 shifts used to fit
Zeeman:
// and  of R(4), 71 shifts used to fit
 [18404](=)5-X(1) (=)4, (0,0): P, Q, R
Stark:
// of R(4), Q(5) and P(6), 97 shifts to fit
Zeeman: // and  of R(4), Q(5) and P(6), 154 shifts to fit
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Optical Stark spectra of R(4) and R'(4) of UO
(A) R(4)
Zero Field
30MHz
-4
0
+4
MJ=0
E=706V/cm, //
(B) R(4)
Zero Field
0
-4
+4
MJ=0
E=706V/cm, //
-500
-300
-100
+100
Stark Shift (MHz)
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+300
+500
Zeeman effect in R(4) line of UO
(a) Zero Field
MJ=0
(b) B=530G, //
(c) B=530G, 
MJ=+1
MJ=-1
-800
-400
0
Zeeman Shift (MHz)
-8-
+400
+800
Zeeman effect in R'(4) line of UO
(a) Zero Field
-4
0
+4
MJ=0
(b) B=300G, //
(c) B=300G, 
MJ=-1
-4
+4
0
-4
0
Zeeman Shift (MHz)
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+4
MJ=+1
Stark Analysis
The Stark shifts (first-order perturbation theory H=-mE ):
 μEM J Ω
Stark 
(0.5034MHz/D)
J(J  1)
Results
State
m  (D)
X(1)4
3.363(26)
1.00
Un-primed 2.684(31)
0.95
1.00
Primed
0.93
0.89
3.110(24)
Correlation Matrix
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Std. dev (MHz)
7.2
1.00
7.3
Zeeman Analysis
The Zeeman shifts (first-order perturbation theory H=-mB):
Zeeman  μB BM J
g eff
J ( J  1)
(MHz )
Results
State
geff
X(1)4
2.562(12)
1.00
Un-primed 3.508(14)
0.90
1.00
Primed
0.89
0.80
4.837(13)
Correlation Matrix
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Std. dev.(MHz)
9.2
1.00
9.3
Is LFT consistent with the measured m(X(1)4) value?
LFT m(UO)  m(NdO)
NdO: 3.31D
UO (observed ground state): 3.363D
Supports the validity of LFT model for early actinide oxides!
NdO
Also notice:
Krauss et al predicted m of UO for U2+(5f37s, 5I)O2- is 3.86D.
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Is LFT consistent with the measured geff(X(1)4) value?
LFT (Kaldin&Heaven)X(1)4 = 84.5% U2+(5f37s, 5I4)O2- + 15.4% U2+(5f27s2, 3H4)O2-
 J a (J a  1)  L(L  1)  S(S  1) 

g(L, S, J a , )  1 
2J a (J a  1)


Hund’s Case c:
L
S
Ja

g
5f37s (5I4)
6
2
4
4
2.40
5f27s2 (3H4)
5
1
4
4
3.20
Eq. 1 geff(LFT) = 0.8452.40 + 0.154 3.20 = 2.521
The measured geff = 2.562 !
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Eq.1
Concluding Remarks
 The permanent dipole moment and magnetic g-factor have
been measured for the ground state of UO: m=3.363D;
geff=2.562. The values confirm the U2+(5f37s, 5I4)O2- electronic
configuration and the g factor is consistent with the LFT
calculation of the ground state configurational composition.
 Dipole moments and magnetic g-factor were also measured
for two excited states of UO: m=2.684D & 3.110D; geff=3.508 &
4.837. These two excited states exhibit distinctly different
properties, which indicate that dipole moments and magnetic gfactors may be characteristic markers for the electronic
configurations.
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