68th international symposium on molecular spectroscopy ohio state university june 17-21, 2013 wei-li...
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68th International Symposium on Molecular Spectroscopy
Ohio State UniversityJune 17-21, 2013
Wei-Li Li, Tian Jian, Gary V. Lopez, and Lai-Sheng Wang
Department of Chemistry, Brown University, Providence, Rhode Island
UO2−: a Highly Correlated System
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Electronic Structure of the Uranyl: UO22+
Denning, R. G., Electronic structure and bonding in actinyl ions and their analogs. J Phys Chem A 2007, 111 (20), 4125-4143.
Uranyl is one of the most stable uranium compounds in the nature. •U has an formal oxidation state of VI. •Linear structure with two U≡O bonds.
HOMO
]2+[
HOMOs (3σu, 3σg, 1πu, 1πg) has electron density over both U and O atoms, suggesting the U-O bond order. LUMOs (1δu and 1φu) are the 5fδ and 5fφ components of the U 5f shell, non-bonding character.
Fill the LUMO will make the UO2, which was expected to have a 1Σg
+
or 3Φu ground state.
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Photoelectron Spectrum of UO2
Allen, G. C.; Baerends, E. J.; Vernooijs, P.; Dyke, J. M.; Ellis, A. M.; Feher, M.; Morris, A. J Chem Phys 1988, 89, 5363.
FIG. He I photoelectron spectrum of the vapor above an equimolar VO, (s) IV (s) mixture heated to 2250 ± 30 K. Ordinate: Counts. Abscissa: Ionization energy (eV).
UO2
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915 cm-1
UO2 in Neon Matrix
IR Spectrum of UO2
Which is the ground state:
3Φu or 3Hg ?
Hunt, R. D.; Andrews, L. J Chem Phys 1993, 98, 3690Zhou, M. F.; Andrews, L.; Ismail, N.; Marsden, C. J Phys Chem A 2000, 104, 5495.Li, J.; Bursten, B. E.; Andrews, L.; Marsden, C. J. J. Am. Chem. Soc. 2004, 126, 3424.
776 cm-1
UO2 in Argon Matrix
3Φu
3Hg
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FIG. 1. Segments of the REMPI spectrum of UO2 taken in the near UV spectral range. In the gas phase.
Figure 1. Emission spectra for UO2 trapped in solid Ar at 12 K. These traces were recorded using 266 nm excitation. (a) Fluorescence in the 360-440 nm range.
Lue, C. J.; Jin, J.; Ortiz, M. J.; Rienstra-Kiracofe, J. C.; Heaven, M. C. J. Am. Chem. Soc. 2004, 126, 1812.
Electronic Structure of UO2
The ground state is 3Φu.
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What is the ground state of UO2? what is the electronic structure?
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M
M*
VD
E
AD
E
M-
M + e-
e- K
E
Configuration coordinate
Ele
ctro
n B
ind
ing
En
erg
y
h
Detachment continuum
Detaching electron from the anionic ground state to access the neutral ground and excited states. This technique depicts the electronic structures of the neutral species.
Photoelectron Spectroscopy: Principle
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Photoelectron Spectroscopy of Size-selected Clusters
Cu–
LS Wang et al., J. Chem. Phys. 102, 9480 (1995)Laser Vaporizationcluster source
Ion extraction
Time of flight MS
Magnetic-bott
le PES
4s-1 3d-1
4s-1 4p+1
UO2−
The target comes without inert gas protection. The residual oxygen on the uranium target surface is enough to produce the UO2
− cluster.
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Photoelectron Spectra of UO2−
Frequencies:
250 ± 50 cm−1
860 ± 50 cm−1
Binding Energy (eV)
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Theoretical Calculation of UO2− and UO2
Qualitative scalar-relativistic valence orbital energy-level scheme for U and O atoms on the left and right sides, and Dh UO2
in the middle
Non-bonding character.Bonding length does change much upon electron detachment.
Bonding character.
Active space for calculation
U(5f) U(7s) U(5f) + O (2p)
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Photoelectron is one electron process, from the U(7s25f1) configuration, all those electronic configuration are not expected. This suggests very strong auto-excitation happens during the electron detachment process.
Assignment of the UO2− Spectra
Cu–
4s-1 3d-1
4s-1 4p+1
Cu – : [Ar] 3d10 4s2
Corresponding to the Cu : [Ar] 3d10 4p
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Conclusion
• Joint PES and ab initio studies were used to investigate the electronic structures UO2 and UO2
– . • Strong electron correlation effect was first
observed between the 7s electron pair. The PES features due to this correlation effect were semi-quantitative assigned.
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Acknowledgement
Brown University
Gary V. Lopz Tian Jian Lai-Sheng WangTsinghua University
Prof. Jun Li
Dr. Jing Su