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

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


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


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)


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


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


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


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


• Stick spectra showing 3Pi w/1S+

438000 443000 448000 453000 458000 463000

Frequency (MHz)

ZnO (X1+)J = 16 - 17

???


451500 453500 455500 457500 459500 461500 463500 465500

Frequency (MHz)

ZnO (a3Pi) ?

L-doubling


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


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


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}



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


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


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

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

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