1. Main Title Manori Perera 1 and Ricardo Metz University of Massachusetts Amherst 64 th International Symposium on Molecular Spectroscopy June 25th, 2009 1 University of Illinois at Urbana-Champaign Photodissociation Spectroscopy and Dissociation Dynamics of TiO + (CO 2 )

2. 2 Outline  Introduction  Spectroscopy  Instrumentation  Results & Discussion  Summary

3. 3 Introduction  Transition metal oxide cations as catalysts  TiO is used as a non-platinum electro catalyst  To characterize reactions such as methane to methanol conversion Proxima Centauri  To understand the interaction of CO 2 with M + and MO +  M + + CO 2  MO + + CO First oxygen abstraction  MO + + CO 2  MO 2 + + CO Second oxygen abstraction  MO + + CO 2  MO + (CO 2 ) Clustering  Oxo-ligand influence on metal chemistry  Astrophysical importance  Characterization of stars uses TiO  TiO + is of interest to astrophysicists

4. 4 Motivation Behind TiO + (CO 2 )  Ti + - O bond is very strong  Its hard to use photofragment spectroscopy to observe the absorption of TiO + molecule  To understand the excited states of TiO +  Instead of breaking Ti + -O bond, we can use a spy molecule like CO 2  Observe the perturbations due to ligand binding  Electron density changes when TiO + is electronically excited

5. 5 Photofragment Spectroscopy TiO + + CO 2 TiO + (CO 2 ) TiO + (CO 2 ) * h  Information  Electronic spectroscopy  Spectroscopic constants  Dissociation dynamics  Thermodynamics

6. 6 Expected Transitions of TiO + 2 Σ Excited state 1δ 9  2 Π Excited state 1δ 4π 2 Δ Ground state of TiO + 1δ1δ 99 4π4π 3π3π  Allowed transition  Calculated to be ~16600 cm -1  Oscillator strength is zero  CO 2 perturbs - transition allowed  Calculated to be ~11300 cm -1  Photoelectron spectroscopy 11227 cm -1

7. 7 Instrument Make Ion Clusters Monitor Photofragments Mass Spectrometer Select Specific Cluster Size Mass Spectrometer

8. 8 Type of Spectra  Mass Spectrum Intensity (mV) m/z 48 TiO + (CO 2 ) 50 TiO + (CO 2 )  Difference Spectrum  Photodissociation Spectrum

9. 9 Dissociation Pathways of TiO + (CO 2 ) At 630 nm Dissociation Yield Normalized Photofragment Yield (mV) O-Ti +. O=C=O O-Ti + + O=C=O h Fragment TiO + Depleted parent TiO + (CO 2 ) Relative time (  s)

10. 10 Photodissociation Spectrum Relative Time (µs) Photofragment Yield (mV) A fragment A parent Normalized Photofragment Yield A fragment A parent x Laser power

11. 11 Photodissociation Spectrum of TiO + (CO 2 ) Energy (cm -1 ) Normalized TiO + Yield

12. 12 How To Find The Band Origin  Vibrational frequencies depend on the reduced mass of the molecule For a diatomic ω = (k/μ) 1/2 where μ = (m 1. m 2 )/(m 1 + m 2 ) So, ω 50 = 0.994986 ω 48 Isotopes LevelCalculated (cm -1 ) Observed (cm -1 ) 14.412.6 +/- 0.3 29.0810.6 +/- 1.9 313.7613.00 +/- 1.5 Shift of Energy (cm -1 ) Band Number ’ = - 1 ’ = + 1 ’ =

13. 13 Electronic Spectroscopy of TiO + (CO 2 ) Energy (cm -1 ) Normalized TiO + Yield V TiO+ = 0 V TiO+ = 1 V TiO+ = 2 V TiO+ = 3  Perera et al. J. Phys. Chem. A 2009, 113 (22), 6253-6259. 0 cm 1 Shift -1873 cm -1 Shift -2795 cm -1 Shift Normalized TiO + Yield 14000 14250 14500 Energy (cm -1 ) -943 cm -1 Shift Experimental  e = 952 cm -1  e X e = 5 cm -1 T e = 13918 cm -1 Calculated  e = 968 cm -1  e X e = 4.4 cm -1 T e = 14877 cm -1

14. 14 Low Frequency Modes Bend quanta 0 stretch quanta 1 stretch quanta 0 1 2 3 4 2 stretch quanta 0 1 3 stretch quanta 0 1 2 3 4 Energy (cm -1 ) Normalized TiO + Yield Metal-ligand stretch 186 cm -1 Metal-ligand bend 45 cm -1

15. 15 Dissociation Kinetics Time (μs) Dissociation Yield Experimental spectrum at 14204 cm -1 Difference spectrum at 14925 cm -1 Difference spectrum at 14204 cm -1 Normalized TiO + Yield 8 7 6 5 4 3 2 Time (  s) Perera et al. J. Phys. Chem. A 2009, 113 (22), 6253-6259

16. 16 Calculations Bond Length of Ti-O (Å)  B3LYP with a 6-311+G(d,p) basis set  Optimized the geometry  Time dependent DFT Relative Energy (eV) TiO + 2Σ2Σ 22 2Δ2Δ Relative Energy (eV) TiO + 2Σ2Σ 22 2Δ2Δ Bond Length of Ti-O (Å) 2 A”( 2 Δ) 2 A’ ( 2 Σ) 2 A”( 2  ) 2 A’( 2  ) Relative Energy (eV) TiO + 2Σ2Σ 22 2Δ2Δ TiO + (CO 2 )

17. 17 Summary  In the presence of CO 2 the  Miliordos calculation shows ω e = 969 cm-1 and ω e x e = 4.4 cm -1  TiO + excited state binds to CO 2 stronger  Internal conversion is the dissociation mechanism. TiO + (CO 2 )* Observed (cm -1+ ) TiO + (CO 2 )* Calculated (cm -1 ) Calculated TiO + (cm -1 ) Estimated TiO + (cm -1 ) Band origin13918148771638515426 Vibrational frequency 95210331049968

18. 18 Acknowledgement Cast of Characters (left-to-right) Murat Citir, Paul Ganssle, me, Ricardo Metz, Gokhan Altinay Plus: Chris Thompson Funding National Science Foundation

19. Questions?