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!