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Electronic Structure of AlMoO y − (y = 1−4) Determined by Anion Photoelectron Spectroscopy and DFT Calculations Sarah E. Waller 67 th International Symposium.

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Presentation on theme: "Electronic Structure of AlMoO y − (y = 1−4) Determined by Anion Photoelectron Spectroscopy and DFT Calculations Sarah E. Waller 67 th International Symposium."— Presentation transcript:

1 Electronic Structure of AlMoO y − (y = 1−4) Determined by Anion Photoelectron Spectroscopy and DFT Calculations Sarah E. Waller 67 th International Symposium on Molecular Spectroscopy 18 June 2012

2 Transition Metal Oxides Numerous Applications Catalysis Photoelectric Cells Electrochromic Materials Solar Cells Sensors

3 Catalyst-Support Interactions Support substrate can greatly affect catalytic performance Alumina-supported MoO 3 1 Catalytically active sites are difficult to study/optimize Dilution effects Processing variables 1 Singhal et al., Chem. Lett., 37, 620 (2008).

4 Small Clusters Defect sites (local bonding) “Window” into atomic scale interactions Probe molecular and electronic structures Anion Photoelectron (PE) spectroscopy Mass selective Density Functional Theory (DFT) Determine relevant structures Small Cluster Studies

5 Anion Photoelectron Spectroscopy Q sym Anion Ground State Neutral Ground State Neutral Excited State hνhν Energy e − KE 1 e − KE 2 e − KE 3 Access neutral states Δs = ± ½ One e − transition

6 Photoelectron Spectrometer Experimental Components: 1)Cluster Production 2)Mass Separation/Selection 3)Anion Photodetachment Resolution eV at 0.5 eV Decays with

7 PE Spectra of AlMoO y − (y = 1−4) Vibrationally unresolved electronic transitions AlMoO 2 − AlMoO 3 − Cleanly resolved vibrational progressions AlMoO − AlMoO 4 − Monotonic EA a increase AlMoO  AlMoO 2  AlMoO 3  AlMoO 4  e − BE (eV) X A B C X A B X X

8 Computational Methods DFT Calculations Gaussian 09 1 Suite B3LYP SDD pseudopotentials Triple-ζ Level aug-cc-PVTZ Method, basis sets, and troubleshooting advice provided by Professor Raghavachari and group Reconciliation with experiment/quantitative comparison Adiabatic Detachment Energy Vertical Detachment Energy Vibrational frequencies Franck-Condon Simulations 1 M.J. Frisch et al., Gaussian 09, Revision A.1 (2009).

9 Connecting Experiment and Theory FCFGAUS 1 Gaussian output files Franck-Condon overlap Mode frequencies Displacements PESCAL 2 Uses FCFGAUS information Simulate transitions Convolute with Gaussian functions Harmonic oscillator approximation Duschinsky rotations e − BE (eV) K. M. Ervin et al., J. Phys. Chem. A, 105, (2001). 2 K. M. Ervin, PESCAL, Fortran program (2010).

10 Computational Results Anions 0.5 eV of the Lowest Energy Anion Neutrals 2.0 eV of the Lowest Energy Neutral Naming Convention: Example ‘120’ ‘ABC’ Scheme O a MoO b AlO c Mo Al OcOc OaOa ObOb

11 AlMoO − Anion Frequency (cm -1 ) Neutral Frequency (cm -1 ) ΔQ (Å∙amu 1/2 ) e − BE (eV) X A B C Bandβ X1.2 B eV 0.0 eV 4.4 eV 2.3 eV 4.0 eV Σ eV Σ eV Δ 1.62 eV A′ 1.94 eV A′ 1.94 eV A′ (AF) 1.51 eV Σ − 1.91 eV 0.90 eV AlMoO − AlMoO e − BE (eV) 6 Σ + 5 Σ

12 Dashed lines indicate the transition from singly occupied to doubly occupied orbitals. AlMoO − MOs MO Comparison: MoO − R.F. Gunion et al., J. Chem. Phys., 104, 1765 (2006). EA a = 0.95(1) eV 11,500 cm -1

13 AlMoO 2 − Anion Frequency (cm -1 ) Neutral Frequency (cm -1 ) ΔQ (Å∙amu 1/2 ) ; ω e χ e = ; ω e χ e =51.00 Bandβ X0.6 A0.2 B0 1.6 eV 2.8 eV 2.96 eV 3.46 eV 0.0 eV e − BE (eV) 4 A″ 3 A AlMoO 2 − AlMoO 2 X A B e − BE (eV)

14 AlMoO 2 − MOs MO Comparison: MoO 2 − e − BE (eV) AlMoO 2 − (shifted eV) MoO 2 − B.L. Yoder et al., J. Chem. Phys., 122, (2005).

15 AlMoO 3 − Anion Frequency (cm -1 ) Neutral Frequency (cm -1 ) ΔQ (Å∙amu 1/2 ) ; ω e χ e =50.4 e − BE (eV) A′ 1 A′ AlMoO 3 − AlMoO eV 0.7 eV 0.0 eV

16 Anion Frequency (cm -1 ) Neutral Frequency (cm -1 ) ΔQ (Å∙amu 1/2 ) ; ω e χ e = AlMoO 3 − e − BE (eV) A′ 1 A′ AlMoO 3 − AlMoO eV 0.0 eV 2.2 eV

17 AlMoO 3 − MOs MO Comparison: MoO 3 − e − BE (eV) MoO 3 − AlMoO 3 − (shifted eV) R.B. Wyrwas et al., J. Phys. Chem. A, 110, 2161 (2006).

18 AlMoO 4 − Anion Frequency (cm -1 ) Neutral Frequency (cm -1 ) ΔQ (Å∙amu 1/2 ) eV 1.9 eV 3.5 eV Y. Xu et al., Catal. Lett., 40, 204 (1996). e − BE (eV) A 1 1 A 1 Al 2 [MoO 4 ] complex seen in HZSM-5 supported Mo AlMoO 4 − AlMoO 4

19 Conclusions Preferential bonding of oxygen to Mo Mo will compete for O atoms from Al 2 O 3 substrate Mo=O more stable than Al − O bonds HOMOs are Mo-local Except AlMoO 4 − Al-local orbital situated between Mo d-like orbital(s) and O p-like orbitals Ionic bonding between MoO y 2−/− and Al + AlMoO y − Lower e − BEs AlMoO  AlMoO 2  AlMoO 3  AlMoO 4  e − BE (eV) X A B C X A B X X

20 Acknowledgements Dr. Caroline C. Jarrold C.C. Jarrold Group Dr. Jennifer Mann Raghavachari Group Benjamin Gamoke Raghunath Ramabhadram Funding: IU Resources Machine Shop Electronic Shop


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