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The 66th International Symposium
on Molecular Spectroscopy, June 2010
Fang Wang ,Anh Lee and Timothy C. Steimle Dept. Chem. & BioChem., Arizona State University, Tempe, AZ,USA
Funded by: NSF
Spectroscopy of thorium monoxide,ThO
in support of Particle Physics
Michael C. Heaven
Dept. Chem. , Emory University, Atlanta, Georgia, USA
Goals: a)permanent electric dipole momentsa b)Franck-Condon prediction/intensityc) lifetime
Outline
II. Experimental setup
IV. Analysis/Results
III. Observation-Spectraa. Dispersed Fluorescenceb. Lifetime (Decay curve)c. Stark
V. Discussion
I. Motivation
VI. Summary
aF. Wang, A. Lee, T.C.Steimle and M.C. Heaven, J.Chem. Phys, 134, 031102(2011)
MotivationNeeded in scheme to test of elementary particle physics beyond the Standard Model via measurement of electric dipole moment of electron, de.
Chemist’s view of an electron: Point Charge
Physist's view of an electron: Point Charge with distribution
Dipole moment of an electron,
de
Experimental limita: |de| < 1.610-27 ecm
aB. Regan, E. Commins, C. Schmidt, D. DeMille, PRL 88, 071805 (2002) Based on thallium atom.
Note dipole moment of HCl 6 D= 1.210-8e.cm
How big is de? Standard Model de~10-41 e·cm
10-19 times smaller
Amplifying the electric field Eint with a polar molecule
Why ThO?
Energy= -Eint•de Eint
= electric field near the nucleus
Small -doubling
The =1 component of the 3 state is non-magnetic.
Heavy polar molecular:
Smaller systematic errors
The metastable H31 state:
Eint ~ 2Z3 e/a02 ~ 100 GV/cm Polarizability factor
Z: Atomic number
complete polarization with very small fields
Experimental SetupLaser ablation source and supersonic expansion, Laser
Induced Fluorescence (LIF) detector
Well collimatedmolecular beam
Metal target(Th foil)
Pulse valve
skimmerAblation laser
O2
& Ar(carrier gas)
Pulsed dye laser
Single freq. tunable laser radiation
Fluorescence
PMT
Monochromator
PMT
Stark plates
Optical Stark spectroscopy
Excitation spectra
High resolution spectra
Thorium foilO2
DF spectra
Observed electronic states and transitions in ThOG.Edvinsson and A. Lagerqvist(1985)
E(0+)X1
F(0+)X1
F-H3
613nm
545nm
760nmR-H3
G-H3
E&H same Th2+(7s6d)O2− configurationa.
aV.Goncharov, J. Han, L.A.Kaledin, and M.C.Heaven, J.C.P 122,204311(2005)
Pulsed Dye Laser Observation: Excitation & DF
P-branch R-Branch
17145.4cm-1
DF Spectra
P-branch R-Branch
18337.5cm-1
Excitation Spectra
Excitation Spectra
DF Spectra
E(0+)<---X1(1,0)
F<---X1(0,0)
”
0
10
’
Laser
”
’1
3210
Laser
Lifetime measurement
E(0+)-X1()
F(0+)-X1()
Laser
decay
Laser
decay
High Resolution: R(0) E-X Field Free & StarkHigh Resolution: R(0) E-X Field Free & Stark
ac
b
E=0V/cmE=3600.7V/cm
E=0V/cmE=3662.4 V/cm
1) Franck-Condon factor prediction
Prof. LeRoy’s Suite of Program: “RKR1 v2.0” & “Level v8.0”
1,0 1,1 1,2 1,3
E(0+)-X1+ 0.135 0.602 0.233 0.0286
0,0 0,1 0,2 0,3
F(0+)-X1+ 0.829 0.149 0.0211 0.0015
(0,0)
(0,1)
F1(0+)-X1()
E1(0+)-X1()
(1,0)(1,1)
(1,2)(1,3)
Analysis/Results
Fit to:Four parameters:y0, A1, x0, 1
1 is lifetime
2) Radiative lifetime measurement
E(0+)-X1()F(0+)-X1()
1=0.2594(5) s1=0.574(9) s
Analysis/Results (Conti.)
1,0(E-X) < 1.56 D
0,0(F-X)≈0.95 Di is radiative lifetime for the upper level, A is the Einstein spontaneous emission coefficients, is the transition dipole moment(Debye),is the transition frequency(cm-1).
Analysis of FF & Stark Spectrum of E-X (1,0)
(case(a))SJ>Basis function:
HRot=BJ2
Field-Free Spectrum T10 =17144.98069(36) cm-1; B”= 0.331967(27) cm-1 ; B’= 0.321185(27) cm-1
Stark Spectrum 88 representation ( J=0-7)
(X1+) = 2.782 (12) D
(E(+)) = 3.534 (10) D
DiscussionPermanent electric dipole moment
The larger dipole moment of the E state r esult s f rom the cir cumst ance that the 6d orbit al is less polar izable than the 7S .
LessPolarizable
Theorya 1
3.9(CASSCF)
Theoryb 2
2.93(RCCSD(T))
aC. M. Marian, U. Wahlgren, O. Gropen, and P. Pyykko, THEOCHEM 46, 339 (1988).bA.A. Buchahenko,J. Chem. Phys. 133, 041102(2010)
Th2+(7s6d)O2
−
Th2+(7s2)O2−
Summary and Future work
a) Franck-Condon prediction matches the experimental intensity pretty well.
b) The lifetimes for F(0+)-X1+(0,0) and E(0+)-X1+(1,0) bands are measured. The transition moments were estimated for both bands.
c) Dipole moments were determined for both E(0+) and X1+ states. The dipole moment for the H31 state will be approximately that of the E(0+) state because the two states are derived from the same Th2+(7s6d)O2−
configuration.
d) Different production methods need to tried to pumping ThO molecules to the metastable H31 state. (e.g. Dicharge source)
e) Other thorium containing molecules can also be tried: ThC,ThSi.
Thank you!