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!!!
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