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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 )
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2 Outline Introduction Spectroscopy Instrumentation Results & Discussion Summary
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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
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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
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5 Photofragment Spectroscopy TiO + + CO 2 TiO + (CO 2 ) TiO + (CO 2 ) * h Information Electronic spectroscopy Spectroscopic constants Dissociation dynamics Thermodynamics
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6 Expected Transitions of TiO + 2 Σ Excited state 1δ 9 2 Π Excited state 1δ 4π 2 Δ Ground state of TiO + 1δ1δ 99 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
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7 Instrument Make Ion Clusters Monitor Photofragments Mass Spectrometer Select Specific Cluster Size Mass Spectrometer
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8 Type of Spectra Mass Spectrum Intensity (mV) m/z 48 TiO + (CO 2 ) 50 TiO + (CO 2 ) Difference Spectrum Photodissociation Spectrum
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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)
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10 Photodissociation Spectrum Relative Time (µs) Photofragment Yield (mV) A fragment A parent Normalized Photofragment Yield A fragment A parent x Laser power
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11 Photodissociation Spectrum of TiO + (CO 2 ) Energy (cm -1 ) Normalized TiO + Yield
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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 ’ =
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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
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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
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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
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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 22 2Δ2Δ Relative Energy (eV) TiO + 2Σ2Σ 22 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 22 2Δ2Δ TiO + (CO 2 )
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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
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18 Acknowledgement Cast of Characters (left-to-right) Murat Citir, Paul Ganssle, me, Ricardo Metz, Gokhan Altinay Plus: Chris Thompson Funding National Science Foundation
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