June 22-26, 200964th International Symposium on Molecular Spectroscopy
The Pure Rotational Spectrum of ZnO in the excited a3Pi State
Lindsay N. Zack, Robin L. Pulliam, and Lucy M. Ziurys
University of Arizona, Department of Chemistry, Department of Astronomy, Steward Observatory, Arizona
Radio Observatory, Tucson, AZ
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Why the Interest in ZnO?• Relevant to several different fields
– Inorganic Chemistry: catalysis– Organic Chemistry: synthesis– Materials Science: semiconductors, thin
films, solar cells– Photoconduction– Nanotechnology
• Everyday use– Sunscreen– Vitamins
1) Sofos et al., Nature Materials (2009), 8, 65-752) Sharghi et al., Synthesis (2002) 1057-1059
1)
2)
3)
3) Wang et al., Appl. Phys. Lett. 84, 4941 (2004); DOI:10.1063/1.1760594
June 22-26, 200964th International Symposium on Molecular Spectroscopy
ZnO• In 2008, pure rotational spectrum of ZnO in ground electronic state
measured by Zack et al.
• All diatomic 3d transition metal oxides have now been studied with high-resolution spectroscopy in the ground state
• Most previous studies of ZnO have focused on its bulk properties- dielectric constant and bandgap energy have been determined (eg. Singh 2007)
• PES (Moravec 2001; Kim 2001; Fancher 1998) and FTIR (matrix) (Chertihin 1996) have been used to determine the equilibrium bond lengths and vibrational frequencies
• Predictions of low-lying a3P excited state, ~2000 cm-1 (Baushlicher and
Partridge, 1998)
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Direct-absorption mm/sub-mm wave spectrometer• Radiation Source: Phase-locked Gunn oscillators and Schottky diode multipliers (65-850 GHz)• Gaussian beam optics utilized to minimize radiation loss• Reaction Chamber: water cooled with br• Detector: InSb bolometer• Radiation is modulated at 25kHz and detected at 2f
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Molecular Synthesis• Gas-phase synthesis• Zinc vapor produced in Broida-type oven
– Alumina crucible in tungsten wire basket– m.p. 420 C
• Reactant gas (N2O) added over top of oven• Argon carrier gas• d.c. discharge needed
(250 mA at 200 V)
Problems• Zinc coats optics• Solids build-up inside reaction chamber
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Frequency (MHz)478420 478475 478530 478585
67ZnOv = 1
70ZnOv = 0
64 ZnOv = 2
ZnO (X1+): J = 17 18
486777 486832 486887
64ZnOv = 0
64Zn 66Zn 67Zn 68Zn 70Zn48.6% 27.9% 4.1% 18.8% 0.6%
Zack et al., J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.04.001
June 22-26, 200964th International Symposium on Molecular Spectroscopy
438 443 448 453 458Frequency (GHz)
ZnO (X1+)J = 16 - 17
70ZnO
v = 067ZnO
v = 1
64ZnO
v = 2
67ZnO
v = 2
68ZnO
v = 2
64ZnO
v = 366ZnO
v = 2
68ZnO
v = 1
66ZnO
v = 364ZnO
v = 4
68ZnO
v = 3
66ZnO
v = 4
68ZnOv = 4
66ZnO
v = 167ZnO
v = 0
68ZnO
v = 0
64ZnO
v = 1
66ZnO
v = 0
64ZnO
v = 0
• Five isotopologues• Several vibrational satellite lines•19 lines per transition
June 22-26, 200964th International Symposium on Molecular Spectroscopy
• Stick spectra showing 3Pi w/1S+
438000 443000 448000 453000 458000 463000
Frequency (MHz)
ZnO (X1+)J = 16 - 17
???
June 22-26, 200964th International Symposium on Molecular Spectroscopy
451500 453500 455500 457500 459500 461500 463500 465500
Frequency (MHz)
ZnO (a3Pi) ?
L-doubling
June 22-26, 200964th International Symposium on Molecular Spectroscopy
ZnO (a3Pi)
= 2
= 1
= 0
J + 1
J e
ef
f
ef
f
f
e
f
e
e
selection rules: = 0J = ±1e f
EJ + 1
J
J + 1
J
June 22-26, 200964th International Symposium on Molecular Spectroscopy
457836 457886 457936 461904 461954 462004 465388 465438 465488
= 2 = 1 = 0e
eef f
f
J = 20 ← 19
ZnO (a3Pi)
• All three spin orbit components identified• Inverted state • Lambda-doubling observed as expected in each
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Zack et al., J. Mol. Spectrosc. (2009), doi: 0.1016/j.jms.2009.04.001
June 22-26, 200964th International Symposium on Molecular Spectroscopy
AnalysisHeff = Hrot + HSO +HSS + Hld
= B (J-S)2 – D (J-S)4 + A (L•S) +
½ AD {L•S, (J-S)2} + 2/3 λ (3Sz2-
S2) + 1/3 λ D {(3Sz2-S2)/3, (J-S)2} –
½ (p+2q)(J+S+ + J-S-) + ¼
(o+p+q)D{(S+2+S-
2) , (J-S)2} –
¼ (p+2q)D{(J+S+ + J-S-) , (J-S)2}
+ ¼ qD{ (J+2 + J-
2) , (J-S)2}
Zack et al., J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.04.001
June 22-26, 200964th International Symposium on Molecular Spectroscopy
ZnO (a3Pi) Equilibrium Constants
Equilibrium parameters for 64ZnO (3Pi)This work PES exp.* Theory**
Be (MHz) 11 622.0636(72)ae (MHz) 120.3980(91)De (MHz) 0.02212(10)be (MHz) -0.000224(12)re (Å) 1.8436(2) 1.850 1.827 – 1.873we (cm-1) 562 540 - 550 525 - 590wexe (cm-1) 4.76 4.36 – 4.76DE, v =0 (eV) 2.02 1.36 1.14 – 1.38
** [1] C.W. Bauschlicher Jr. and H. Partridge, J. Chem. Phys. 109 (1998), pp. 8430–8434; [2] S. Boughdiri, B. Tangour, C. Teichteil, J. Barthelat and T. Leininger, Chem. Phys. Lett. 462 (2008), pp. 18–22; [3] J.F. Harrison, R.W. Field and C.C. Jarrold, ACS Symp. Ser. 828 (2002), pp. 238–259
* [1] V.D. Moravec, S.A. Klopcic, B. Chatterjee and C.C. Jarrold, Chem. Phys. Lett. 341 (2001), pp. 313–318; [2] J.H. Kim, X. Li, L.-S. Wang, H.L. de Clercq, C.A. Fancher, O.C. Thomas and K.H. Bowen, J. Phys. Chem. A 105 (2001), pp. 5709–5718
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Conclusions• Identified a3Pi state in ZnO• Observed all three spin components• Lambda-doubling resolved in all three components• Established rotational, spin-orbit, spin-spin, and lambda-
doubling constants• Determined equilibrium parameters• re, we, and wexe agree well with previous experimental
and theoretical work• This work suggests DE, v =0 = 2.02 eV for Morse potential
June 22-26, 200964th International Symposium on Molecular Spectroscopy
Acknowledgements• Lucy Ziurys• Lindsay Zack• Leah O’Brien• Rest of Ziurys Group
DeWayne Halfen Emily TenenbaumMing Sun Gilles AdandeJessica Dodd Matthew BucchinoJie Min Brent Harris
• NSF and NASA - Funding