1. Threshold Ionization and Spin-Orbit Coupling of CeO
Wenjin Cao, Yuchen Zhang, Lu Wu, and Dong-Sheng Yang
Department of Chemistry
University of Kentucky

2. Motivations CeO vs. LaO Ce 6s14f1 vs. La 6s1 CeO+ vs. LaO+
Metal oxides are widely used as catalysts or catalyst supports.
Small metal oxides are the building blocks of nanoparticles and show size- dependent properties.
Our group has recently studied several small LanOm clusters.
42300
874
812
CeO vs. LaO
Ce 6s14f1 vs. La 6s1
CeO+ vs. LaO+
Ce 6s04f1 vs. La 6s0
L. Wu, et al., J. Chem. Phys. 137, (2012)
L. Wu, et al., J. Chem. Phys. 140, (2014)

3. Previous Measurements
In the 1970s, CeO was identified in the absorption spectra of S-type stars and attentions started to be drawn on the studies of CeO molecule.
Most comprehensive measurements by Linton, Field and coworkers using LIF:
Accurate energies of low-lying excited states in the ranges of and cm-1.
Vibrational and rotational constants for different electronic states.
Systematic nomenclature for the excited states based on total angular momentum quantum number J and the projections Ω.
R. F. Barrow, et al., Astrophys. J. 229, 439 (1979)
C. Linton, et al., J. Chem. Phys. 74, 189 (1981)
C. Linton, et al., J. Mol. Spectrosc. 102, 441 (1983)

4. Previous Calculations
Dolg and co-workers
quasirelativistic pseudopotential CI methods.
Tatewaki and co-workers
restricted active space CI (RASCI) calculations with four-component relativistic effect.
M. Dolg, et al., J. Mol. Struct. 231, 243 (1991)
H. Moriyama, et al., J. Chem. Phys.,138, (2013)

5. Experimental Setup Detector TOF Tube Extraction Can PV GV HV He/Ar UV
320 V/cm
532 nm
Diffusion Pump
Turbo pump
Reaction Chamber
Spectroscopy Chamber

6. Computational Details
Software: GAMESS 2016 R1
Geometry optimization and frequency analysis: completely renormalized (CR)-CCSD(T)
Locating spin-orbit states:
Reference states (7 singlet states and 7 triplet states for neutral CeO, and 7 doublet states for corresponding cation) calculated by CI.
State energies located by spin-orbit coupled multiconfiguration quasi-degenerate perturbation theory (SO-MCQDPT) calculations.
Relativistic Effect: local unitary transformation approximation for the infinite order two component transformations (LUT-IOTC)
Basis Set: Quadruple ζ-quality core-correlating all-electron basis sets of Noro and co-workers

7. MATI Spectrum & Calculated Structure
43015
E0 (cm-1)
R (Å)
ωe (cm-1)
Neutral
1.822
826
Cation
42897
1.776
890

8. Possible Transitions A+ X+ X+ v=2 v=2 v=2 v=1 v=1 v=1 A X B
X, A, B: Ground state, 1st, and 2nd excited states of the neutral
X+, A+: Ground state and 1st excited state of the cation A+ X+ X+
v=2
v=2
v=2
v=1
v=1
v=1 A X B

9. 43015
817
890 85
1672
1860
Transitions from 2 lowest neutral states to 1st ionic excited state.
1920
2148
2050
2627
665
2775

10. Measured and Calculated Energies
Neutral
Cation
Expt.
SO-MCQDPT 85 86
665
663
817*
828 -
1609
902*
935
2099
1672
1834
1860
2009
1920
2072
2050
2075
2148
2193
2627
2662
2775
2819

11. Comparisons a C. Linton, et al., J. Mol. Spectrosc. 102, 441 (1983)
MATI
Linton, et al.a
RASCIb
SO-MCQDPT
Cation
[43.7]3/2
43680 -
43562
[43.0]5/2
43015
42900
Neutral
W42
2775
2771.7
2527
2819
W33
2627
2617.3
2381
2662
X43
2148
2140.6
2145
2193
X34
2050
2039.8
2025
2075
U10+
1920
1931.8
1100
2072
V21
1860
1869.7
959
2009
V10-
1672
1679.4
742
1834
W22
902*
912.2
615
935
W11
817*
811.6
493
828
X23 85
80.3
110 86
X12
a C. Linton, et al., J. Mol. Spectrosc. 102, 441 (1983)
b H. Moriyama, et al., J. Chem. Phys.,138, (2013)

12. Summary
11 low-lying electronic states for CeO neutral molecule due to spin-orbit effect and 2 for the corresponding cation.
Vibrational frequencies for both neutral and cation, but intensities do not follow FC principle.
Bond lengths predicted to be Å for the neutral and Å for the cation.
Valence electron configurations are Ce 4f16s1,for neutral CeO and Ce 4f1 for the cation.
MATI experiment combining with SO-MCQDPT calculation is a powerful method in identifying the energy splitting due to spin-orbit effect.
Thank You