June 22-26, th International Symposium on Molecular Spectroscopy The Pure Rotational Spectrum of ZnO in the excited a 3  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

June 22-26, th 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, ) Sharghi et al., Synthesis (2002) ) 2) 3) 3) Wang et al., Appl. Phys. Lett. 84, 4941 (2004); DOI: /

June 22-26, th 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 a 3  excited state, ~2000 cm -1 (Baushlicher and Partridge, 1998 )

June 22-26, th International Symposium on Molecular Spectroscopy Direct-absorption mm/sub-mm wave spectrometer Radiation Source: Phase-locked Gunn oscillators and Schottky diode multipliers ( 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, th 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 (N 2 O) 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, th International Symposium on Molecular Spectroscopy 64 Zn 66 Zn 67 Zn 68 Zn 70 Zn 48.6%27.9%4.1%18.8%0.6% Zack et al., J. Mol. Spectrosc. (2009), doi: /j.jms

June 22-26, th International Symposium on Molecular Spectroscopy ZnO (X 1  + ) J = ZnO v = 0 67 ZnO v = 1 64 ZnO v = 2 67 ZnO v = 2 68 ZnO v = 2 64 ZnO v = 3 66 ZnO v = 2 68 ZnO v = 1 66 ZnO v = 3 64 ZnO v = 4 68 ZnO v = 3 66 ZnO v = 4 68 ZnO v = 4 66 ZnO v = 1 67 ZnO v = 0 68 ZnO v = 0 64 ZnO v = 1 66 ZnO v = 0 64 ZnO v = 0 Five isotopologues Several vibrational satellite lines 19 lines per transition

June 22-26, th International Symposium on Molecular Spectroscopy Stick spectra showing 3Pi w/1S+ ZnO (X 1  + ) J = ???

June 22-26, th International Symposium on Molecular Spectroscopy  -doubling

June 22-26, th International Symposium on Molecular Spectroscopy ZnO (a 3  i )  = 2  = 1  = 0 J + 1 J e e f f e f f f e f e e selection rules:  = 0  J = ±1 e  f E J + 1 J J

June 22-26, th International Symposium on Molecular Spectroscopy  = 2  = 1  = 0 e e e f f f J = 20 ← 19 ZnO (a 3  i ) All three spin orbit components identified Inverted state Lambda-doubling observed as expected in each

June 22-26, th International Symposium on Molecular Spectroscopy Zack et al., J. Mol. Spectrosc. (2009), doi: /j.jms

June 22-26, th International Symposium on Molecular Spectroscopy Analysis H eff = H rot + H SO +H SS + H ld = B (J-S) 2 – D (J-S) 4 + A (LS) + ½ A D {LS, (J-S) 2 } + 2 / 3 λ (3S z 2 - S 2 ) + 1 / 3 λ D {(3S z 2 -S 2 )/ 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 q D { (J J - 2 ), (J-S) 2 } Zack et al., J. Mol. Spectrosc. (2009), doi: /j.jms

June 22-26, th International Symposium on Molecular Spectroscopy ZnO (a 3  i ) Equilibrium Constants Equilibrium parameters for 64 ZnO ( 3  i ) This workPES exp. * Theory ** B e (MHz) (72)  e (MHz) (91) D e (MHz) (10)  e (MHz) (12) r e (Å)1.8436(2) –  e (cm -1 )  e x e (cm -1 ) – 4.76 D E, v =0 (eV) – 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, th International Symposium on Molecular Spectroscopy Conclusions Identified a 3  i 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 r e,  e, and  e x e agree well with previous experimental and theoretical work This work suggests D E, v =0 = 2.02 eV for Morse potential

June 22-26, th International Symposium on Molecular Spectroscopy Acknowledgements Lucy Ziurys Lindsay Zack Leah O’Brien Rest of Ziurys Group DeWayne HalfenEmily Tenenbaum Ming SunGilles Adande Jessica DoddMatthew Bucchino Jie MinBrent Harris NSF and NASA - Funding