1. Spectroscopy, Structure, and Ionization Energy of BeOBe
Jeremy M. Merritt,
Vladimir E. Bondybey,
and Michael C. Heaven

2. Background
BeO is a strongly bound, closed-shell molecule. Formally the 2s electrons of Be are donated to the 2p obitals of O. Why would BeO bind a second Be atom?
Previous experiments show that Be2O is stable.
L. Theard and D. Hildenbrand, J. Chem. Phys. 41(11), 8689 (1964)
Heat of Formation of Be2O(g) by Mass Spectrometry
C. Thompson and L. Andrews, J. Chem. Phys. 100(12), 8689 (1994)
Recorded IR spectra in an Ar matrix; nas = cm-1
Theoretical calculations show that the ground state
is multi-configurational.
A. Boldyrev and J. Simons, J. Phys. Chem. 99, (1995)
Multi-Reference Ab initio study

3. Theoretical Predictions
Andrews
MP2
6-311G*
Simons
6-311+G*
QCISD
QCISD(T)
6-311+G(2df)
BeOBe 1Sg+
5752
6051
1399
BeOBe 3Su+
1329
BeBeO 1S+
27013
26196 -
BeBeO 3S+
52922
41935
BeOBe
C2v, 1A1
5384
5211
Not stable

4. Ab Initio calculations for BeOBe – Present Study
New Multi-Reference Calculations
Ab Initio calculations for BeOBe – Present Study
CASSCF/MRCI
aug-cc-pVTZ
X 1Sg+ = 0.73|3sg2 4sg2 1pu4> |3sg2 3su2 1pu4>
3su = 0.87e
pu x 2 = 1.97e
4sg = 1.13e
RBeO = Å B” = cm-1

5. Singlet-triplet splitting for BeOBe
FV-CASSCF/ MRCI(2,2)
D=249 cm-1
FV-CASSCF/ MRCI(10,12)
D=39 cm-1

6. Low Resolution REMPI Spectrum of BeOBe

7. Statistics confirm X state is 1Sg+ P12 Ytot = - Ytot (fermions)
b = |1/2>
c = |-1/2>
d = |-3/2>
Ytot = Yrot Yspin
Jeven: Jodd = 3:5
Statistics confirm
X state is 1Sg+

8. Room temperature spectrum of the BeOBe origin band
l-type doubling
Data taken in an effusive ablation source

9. Trial assignment scheme for band groupingsPg A
Fails because - Su
1. Combination difference
error is too large
2. Upper state perturbation in
the P-S band is not seen in
the P-P band. Pu X Sg

10. Spectroscopic constants for the electronically excited state of BeOBe we
723.6
717.2
wexe
15.2
15.0
DG1/2(2)
69.7 -
DG1/2(3)
788
722.0 B0
0.4584
0.458
ae(1)
0.0068

11. Excited state energies for BeOBe

12. Ground state energy level structure
Dispersed fluorescence
Stimulated emission pumping

13. Observed and calculated vibration frequencies for BeOBe(X)
Vibrational Mode
Observeda
MRCISD+Qb
MP2(full)c
QCISD c
MP2d v1
1039
1065
974
1018
1027 v2
113
125
112 43 76 v3
1414
1468
1452
1436
1418
a. All frequencies are in units of cm-1. The experimental frequencies are approximated by the intervals.
b. Present study.
c. Boldyrev and Simons
d. Thompson and Andrews. These constants are for the triplet state, which was the ground state for this level of theory.

14. Photoionization efficiency determination of the ionization energy
Determining the IE of Be2O; Photo-ionization Efficiency (PIE) Curves
Photoionization efficiency determination
of the ionization energy
Be2O+ + e-
scan
A(v=1)
fix
X (v=0)
Be2O IE = 8.12(1) eV
CCSD(T)
IPa = eV
Tune 1st laser off resonance
MRCI(SD)
IPa = eV

15. Conclusions Spectra for BeOBe establish a linear X1Sg+ ground state.
Ab initio calculations indicate a strongly multi-reference
ground state.
Electronically excited state is A1Su+.
Vibronic structure indicates that levels from a second
excited state are also present in the A-X system.
Ionization energy is 8.12 eV. MRCI calculations are
in good agreement .