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The Pure Rotational Spectrum of ZnO in the excited a 3 P i State

The Pure Rotational Spectrum of ZnO in the excited a 3 P i 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 . Why the Interest in ZnO ?.

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The Pure Rotational Spectrum of ZnO in the excited a 3 P i State

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  1. 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

  2. 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) 3) 2) 3) Wang et al., Appl. Phys. Lett. 84, 4941 (2004); DOI:10.1063/1.1760594 1) Sofos et al., Nature Materials (2009), 8, 65-75 2) Sharghi et al., Synthesis (2002) 1057-1059

  3. 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 a3 excited state, ~2000 cm-1 (Baushlicher and Partridge, 1998)

  4. 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

  5. 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

  6. Zack et al., J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.04.001

  7. 64ZnO v = 0 ZnO (X1+) J = 16 - 17 66ZnO v = 0 • Five isotopologues • Several vibrational satellite lines • 19 lines per transition 70ZnO v = 0 68ZnO v = 0 67ZnO v = 1 67ZnO v = 2 64ZnO v = 3 66ZnO v = 1 64ZnO v = 1 66ZnO v = 3 68ZnO v = 1 64ZnO v = 2 67ZnO v = 0 66ZnO v = 2 68ZnO v = 2 68ZnO v = 4 66ZnO v = 4 68ZnO v = 3 64ZnO v = 4

  8. ZnO (X1+) J = 16 - 17 • Stick spectra showing 3Pi w/1S+ ???

  9. L-doubling

  10.  = 0  = 1  = 2 ZnO (a3i) e J + 1 f selection rules:  = 0 J = ±1 e  f f J e f J + 1 e E e J f e J + 1 f f J e

  11. ZnO (a3i) J = 20 ← 19 W = 2 W = 1 W = 0 e e f f e f • All three spin orbit components identified • Inverted state • Lambda-doubling observed as expected in each

  12. Zack et al., J. Mol. Spectrosc. (2009), doi: 0.1016/j.jms.2009.04.001

  13. Analysis Heff = Hrot + HSO +HSS + Hld = B (J-S)2 – D (J-S)4 + A (L•S) + ½ AD {L•S, (J-S)2} + 2/3λ (3Sz2-S2) + 1/3λ 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

  14. ZnO (a3i) Equilibrium Constants ** [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. A105 (2001), pp. 5709–5718

  15. 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

  16. Acknowledgements • Lucy Ziurys • Lindsay Zack • Leah O’Brien • Rest of Ziurys Group DeWayne Halfen Emily Tenenbaum Ming Sun Gilles Adande Jessica Dodd Matthew Bucchino Jie Min Brent Harris • NSF and NASA - Funding

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