Search for the low-lying electronically excited states

of UO2

Ivan O. Antonov, Michael C. Heaven

Emory University, Department of Chemistry1515 Dickey Drive, Atlanta GA 30322

Motivation

Nuclear waste disposal and reprocessing

Why UO2 is interesting

(I. Infante et al. JCP, 127, 124308 (2007))

DG1/2 = 914 cm-1 (Ne), 776 cm-1 (Ar) Ground state configuration 5f7s 5f2

(Zhou, Andrews, Ismail & Marsden JPCA, 104, 5495 (2000))

5f7s

5f5/2

5f7/2

Ω=2Ω=3

Ω=3Ω=4

How widely are the 3Φu and 3Hg states split???

Difficulties

UO2 exhibits delayedionization near the IP threshold

7.2 7.4 7.6 7.8 8.0 8.2

Ion c

ounts

(ar

b u

nit

s)

TOF (s)

Extremely large density of states!!!

ZEKE spectrum of UO2+

is highly congested

18000 19000 20000 21000 22000

-700

0

Inte

nsit

y (a

rb u

nits

)

2nd photon energy (cm-1)

(Merritt J.M., Han J., Heaven M.C., JCP, 128, 084304 (2008))

Planned experiments

Dispersed fluorescence from previously observed electronically excited states

1+1’ REMPI with first photon in red-NIR

SEP spectroscopy

Experimental setup

1064 nm, 26 mJ

He with 0.1% O2

Ablation

Probe laser(s)

PMT MCP

Probe laser

TOF mass-specOscilloscop

e

Monochromator

Ablationlaser

Emission of UO2 at 31000 cm-1 excitation

X

3Φg

Emission

Excitation

V=1

Emission of UO2 at 27000 cm-1 excitation

X

3Φg

Excitation

2nd order of monochromator

Emission

SEP

X

3Φg

Tunable ND:YAG pumped dye laser

t

Flu

ores

cenc

e

SEP allows probing theground state

SEP on UO2 failed due to state mixing!

REMPI of UO2 in red-NIR region

X

UO2++e

Tunable ND:YAG pumped dye laser

248 nm KrF

Comparison with theory

(I. Infante et al. JCP, 127, 124308 (2006))

Experiment IHFSCC 40 e

2 900 – 4 700 cm-1

1u at 2 231 cm-1

2u at 2 588 cm-1

4u at 5 047 cm-1

7 400 cm-1 2u at 7 431 cm-1

10 900 cm-1 4g at 10 914 cm-1

11 500 cm-1 0g at 11 436 cm-1

12 200 cm-1 1g at 12 564 cm-1

12 900 cm-1 2g at 12 958 cm-1

13 600 cm-1 1g at 13 919 cm-1

14 300 cm-1

1g at 13 919 cm-

1or 5g at 15 408 cm-1

Conclusions

UO2 molecule was studied by REMPI at 10800 – 14600 cm-1 and by dispersed fluorescence on 31800 cm-1 and 27100 cm-1 transition

New excited states were found and preliminarily assigned at 2900-4700 cm-1, 7400 cm-1 and 10900-14300 cm-1 region

Excited state mixing phenomena is responsible for severe line broadening and background signal; It prevents from obtaining rotationally resolved spectra of UO2

Future plans

1+1’ REMPI with OPO/OPA system in mid-IR

X

UO2++e

OPO/OPA

Tunable ND:YAG pumped dye laserat ~ 210-220 nm

Acknowledgements

Vladimir E. Bondybey for help with experiment

Group members: Beau Barker, Jiande Han, Keith Freel and Humayun Kabir

Prof. Michael Heaven

DOE for funding!!!