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High Resolution Electronic Spectroscopy of 9-Fluorenemethanol (9FM) in the Gas Phase Diane M. Mitchell, James A.J. Fitzpatrick and David W. Pratt Department of Chemistry University of Pittsburgh Pittsburgh, PA 15217
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9FM: Two Conformers Symmetric (Sym) Unsymmetric (Unsym) *Naming scheme taken from S. Basu and J. L. Knee. J. Chem. Phys. 120 (2004) 5631.
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Experimental Method Gas phase S 1 S 0 spectroscopy –Low resolution (vibrationally resolved) –High resolution (rotationally resolved) Ab initio calculations using Gaussian 03 –Optimized conformational geometries –Rigid scan of potential energy surface
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PMT Boxcar Integrator Computer Nd 3+ :YAG Laser Dye Laser Low Resolution Apparatus Mirror Filter Iris KDP Crystal He Vacuum Chamber hh
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High Resolution Apparatus 240 m nozzle
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Low Resolution Spectrum unsym sym Band I Band II *Preliminary assignments from S. Basu and J. L. Knee. J. Chem. Phys. 120 (2004) 5631.
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High Resolution Spectra 33788.1 cm -1 33789.5 33560.9 cm -1 33562.5 33562.8 cm -1 33564.4 Band I Band II Band I red Band I blue
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Fit of Band II ~0.08 cm -1 33788.1 cm -1 33789.5
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Key Inertial Parameters *Calculated values computed with MP2/6-31G** and CIS/6-31G** ExperimentalCalculated Band I Red Band I Blue Band II SymUnsym A'' (MHz) 1024.7(2)1025.2(2)936.2(2)1047.7923.1 B'' (MHz) 543.4(1)543.5(1)551.4(1)541.2555.3 C'' (MHz) 392.9(1) 361.3(1)397.1357.5 I'' (amu Å 2 ) -136.8-136.4-57.6-143.5-44.0 A' (MHz) 996.2(2)996.8(2)908.6(2)999.2890.4 B' (MHz) 549.1(1)549.0(1)556.3(1)549.7565.7 C' (MHz) 391.6(1) 359.1(1)395.8356.9 I' (amu Å 2 ) -137.0-136.8-57.4-148.2-44.8 a/b/c 96/2/297/2/1 TM a/b angle (a axis) ±8° Origin (cm -1 ) 33561.733563.633788.8
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Transition Moment Orientation Fluorene 9FM a b b a * Fluorene transition moment orientation from W.L. Meerts, W.A. Majewski, and W.M. van Herpen, Can. J. Phys. 62 (1983) 1293.
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Splitting of Band I 33562.8 cm -1 33564.4 33560.9 cm -1 33562.5 Band I red Band I blue
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Splitting of Band I 1.9 cm -1 (57 GHz) splitting between bands I red and I blue Nearly 1:1 intensity ratio, with band I red being slightly more intense Almost identical rotational constants Two possible explanations –Both are origin bands of two distinct conformations –Symmetric internal motion between two equivalent conformations
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Splitting: Two Different Conformers? Two distinct conformations with similar rotational constants Difference between the transition frequencies is 1.9 cm -1 Small difference in ground state energies can account for nearly 1:1 intensity ratio Conformer A Conformer B S 1 S 0
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Rigid Potential Energy Scan MP2/6-31G 22 11 Starting point: optimized sym geometry 1 and 2 changed in 10° steps No two different minima with sym rotational constants 22 11 Energy
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Splitting: Symmetric Motion? Combined motion of the hydrogen and oxygen Levels split by tunneling Difference in splitting in S 0 and S 1 states results in 1.9 cm -1 splitting between bands 5 exchangeable hydrogen pairs: nearly 1:1 intensity ratio between bands S 0 S 1
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Band II of 9FM has been assigned to an unsym conformation. Band I is split into two: I red and I blue. Both have been assigned to a sym conformation. Transition moment orientation in 9FM is similar to the parent molecule, fluorene. Splitting is explained by conversion between identical conformations via a combined motion of the hydrogen and oxygen above the ring system. Conclusions Opposite of preliminary assignments from REMPI study
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Future Endeavors Obtain spectra of deuterated 9FM (Kraitchman analysis) Run relaxed potential energy surface scan calculations Estimate ground and excited state potential wells based on the 1.9 cm -1 splitting
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Acknowledgements The Pratt Group: Leonardo Alvarez Seung-hoon Hong Cheolhwa Kang Phil Morgan Tri Nguyen Alexei Nikolaev Jessica Thomas John Yi NSF for funding
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Band I red 96/2/2 98/2/0
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High Resolution Ring Dye Laser
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High Resolution Apparatus
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Beam Machine
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Molecular Beam, Source and Collection Optics
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