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

9FM: Two Conformers Symmetric (Sym) Unsymmetric (Unsym) *Naming scheme taken from S. Basu and J. L. Knee. J. Chem. Phys. 120 (2004) 5631.

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

PMT Boxcar Integrator Computer Nd 3+ :YAG Laser Dye Laser Low Resolution Apparatus Mirror Filter Iris KDP Crystal He Vacuum Chamber hh

High Resolution Apparatus 240  m nozzle

Low Resolution Spectrum unsym sym Band I Band II *Preliminary assignments from S. Basu and J. L. Knee. J. Chem. Phys. 120 (2004) 5631.

High Resolution Spectra cm cm cm Band I Band II Band I red Band I blue

Fit of Band II ~0.08 cm cm

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) (2)1025.2(2)936.2(2) B'' (MHz) 543.4(1)543.5(1)551.4(1) C'' (MHz) 392.9(1) 361.3(1)  I'' (amu Å 2 ) A' (MHz) 996.2(2)996.8(2)908.6(2) B' (MHz) 549.1(1)549.0(1)556.3(1) C' (MHz) 391.6(1) 359.1(1)  I' (amu Å 2 ) a/b/c 96/2/297/2/1 TM a/b angle (a axis) ±8° Origin (cm -1 )

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.

Splitting of Band I cm cm Band I red Band I blue

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

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

Rigid Potential Energy Scan MP2/6-31G 22 11 Starting point: optimized sym geometry  1 and  2 changed in 10° steps No two different minima with sym rotational constants 22 11 Energy

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

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

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

Acknowledgements The Pratt Group: Leonardo Alvarez Seung-hoon Hong Cheolhwa Kang Phil Morgan Tri Nguyen Alexei Nikolaev Jessica Thomas John Yi NSF for funding

Band I red 96/2/2 98/2/0

High Resolution Ring Dye Laser

High Resolution Apparatus

Beam Machine

Molecular Beam, Source and Collection Optics