Pump/Probe Microwave-Optical Double Resonance

(PPMODR) Study of Tungsten Carbide( WC)a

and Platinum Carbide(PtC)b

Funded by

Fang Wang, Chengbing Qin, Ruohan Zhang, Timothy C. Steimle

Dept. Chem. & BioChem.,Arizona State University, Tempe, AZ,USA

Funded by

bC. Qin, R. Zhang, F. Wang, T. C. Steimle, Chemical Physics Letters, 535, 2012

aF. Wang and T.C. Steimle, J. Chem. Phys. 136, 044312 (2012).

International Symposium on Molecular Spectroscopy 67th meeting

Outline

I. What is PPMODR?

a). History & Motivation

b). Concepts & Experimental Set-up

a). WC (X3D1)

II. Examples

W-doubling parameter

Observe nearly equal intensity(Magnetic dipole transition VS Electric dipole transition)

b). PtC (X1S+)

Nuclear spin-rotation interaction parameter

182W (26.3%), 183W (14.3%), and 184W (30.1%), 186W (28.6%)

194Pt(33.0%, 195Pt(33.8%) and 196Pt (25.2%)

PPMODR(History)

W.J. Childs, Physics Reports, 211(1992)

Review of Laser-Radiofrequency double resonance studies

S.D.Rosner, T. D.Gaily, and R. A. Holt, Phys. Rev. Lett. 35, 785 (1975)

Molecular-beam, laser-radiofrequency double-resonance(LRDR) technique

Precise ground-state data

W. Ertmer and B. Hofer, Z Phys. A 276, 9(1976)

Hyperfine structure measurements of the atomic beams using the LRDR technique

W.J. Childs, L.S. Goodman: Phys. Rev. A 21, 1216 (1980)

Hyperfine constants of highest precision with the molecular beam using using LRDR technique

W. E. Ernst and S. Kindt, Appl. Phys. B 31( 1983)

A laser-Microwave double-resonance experiment has been developed

LI0 I

Absorption

The intensity is given by Beers Law:

I=I0e-aLC≈I0(1-aLC) Absorption≈aLC

a is molecular absorption coefficientC is the concentration

a∝f*u2f is the fraction of the total which is in the lower of the two states.u is the transition frequency

Laser or Radio-frequency

Line width Dv∝u

Optical spectroscopy & Microwave spectroscopy

High sensitivity, resolution, selectivity

PPMODR(Motivation)

Pump/Probe Microwave-Optical Double Resonance

High absorption High sensitivity

Optical spectroscopy High sensitivity, low resolutionMicrowave spectroscopy low sensitivity, high resolution

Optical spectroscopy

pump

Microwaveradiation

skimmer

Well collimatedmolecular beam

Single freq. tunable laser radiation

PMT

Gated photon counter

W rodor Pt rod

Pulse valve

Ablation laser

CH4(5%)& Ar

PPMODR(Concept)

J”

J’

hulaser

Excitation

J”Radio-frequency

repopulate

Frequency Sythesizer(0~20GHz)

Rubidium frequency standard

homemade E-field horn antenna(3cmX0.4cm)

Active Frequency multiplier 4X or 2X

Magnetic sheild box

FWMH: 50kHz with<<1mW power

PPMODR(Experimental)

Microwave Radiation Source

Pump beam~200mWProbe beam (~20mW)

Laser induced fluorescence(LIF)

Examples 1 WCElectron electric dipole moment(eEDM) MeasurementWC:

1J. Lee, E.R. Meyer, R. Paudel, J.L. Bohn and A.E. Leanhardt, J. Mod. Opt. 56, 2005, (2009).W-doubling õΔ~1kHz

2F. Wang and T.C. Steimle, J. Chem. Phys. 134, 201106 (2011).

W-doubling õΔ<2MHz

Prediction

Optical Spectroscopy

-J=1

J=2X3D1 (v=0) -+

Microwave Frequency(~60GHz)

WC

+W-Doubling

WC – Spectra with PPMODR

LIF

A-J=1

J=2

X3D1 (v=0)

+

-+

[17.6]2(v=1) +/-J=3

CB D

Microwave power:10mWFWHM:400kHz

1.54MHz

2.31MHz

W-doubling õΔ=0.385(13)MHz

Why Imag. ≈ Ielec.?

A. Magnetic dipole transition probability(X3D1)

B. Mix two nearly degenerate energy levels due to stray electric field (W-doublet)

Possible reasons:

Imag. ≈ Ielec.

Rabi frequency welec.=2 *p mab(elec.)*Efield/ha

b

Imag should be small.

. 1009.0elec t . 0.018 1mag t

Microwave power 10mWArea=1.0 cm2

Transit time t=30ms

mab(elec.)=3.90D=1.30*10-29C m

r=3.3*10-7 J/m3P

Area c

Energy density

wRabi

wt≥1 (Rabi frequency and transit time)

Rabi frequency wmag..=2 *p mab(mag.)*Bfield/h

A. Magnetic dipole transition probability (X3D1)

mab(mag.)=(gLL+gsS)mB=0.022mB=2.04*10-25J/TMagnetic dipole moment:L=2,S=-1, gLL+gs =0S

Electric dipole moment:

E-field=273.0V/m0

2Efield

EfieldBfield

c B-field=9.1*10-7 T

Rabi cycles

A. Magnetic dipole transition probability (X3D1)

. 1009.0elec t

. 0.018 1mag t

0.1% mixing of the nearly degenerate W-doublet levels

-J=1X3D1 (v=0)

+ 1.54MHz

12 21

( ) ( / )( ) 0.50348

1JD E V cm M

H H MHzJ J

.

11 12

21 22

1.54 0.9818

0.9818 0

stray

stray

H H E

H H E

ΨN=C+Ψ++ C-Ψ-

Basis function |LSWJMJ>

Estray ≈0.05V/cm

ΨN-=-0.999Ψ--0.032Ψ+

ΨN+=0.032Ψ--0.999Ψ+

0.0322*100%≈0.1%

B. Mix two energy levels due to stray electric field (J=1, W-doublet)

How big is the stray electric field for 0.1% mixing?

m=3.9D

Experimental Pt bonding investigation:

nuclear spin-rotation interaction

Examples 2 PtC

195PtC X1S+ (v=0)

3/2J=1

J=2

1/2

3/25/2

Microwave Frequency(~60GHz)

195Pt(I=1/2)

J=0 1/2

F

Microwave Frequency(~30GHz)

PtC – Spectra with PPMODR

3/2J=1

J=2

X1S+

1/2

3/2

5/2

A1P5/2J=37/2

LIF

195PtC(I=1/2)

A

195PtCA

Cieff=0.138(12)MHz

Summary

PPMODR has been implemented.

Precise W-doubling parameter has been determined

Unusual intensity observed. Possible reasons have been addressed.

Spin-rotation interaction parameter has been determined

WC

PtC

Future Plans: AuX, ThX (X=C, F,O,S)