1. Photoelectron Spectroscopy of Pyrazolide Anion Three Low-lying Electronic States of the Pyrazolyl Radical Adam J. Gianola Takatoshi Ichino W. Carl Lineberger JILA and Department of Chemistry University of Colorado John F. Stanton Institute for Theoretical Chemistry and Department of Chemistry University of Texas

2. Pyrazolide Anion  Prepared by OH  deprotonation of pyrazole  C 2v symmetry  Closed Shell ( 1 A 1 )  Aromatic 6  electrons  Isoelectronic with C 5 H 5 

3. 1a 2 2 2b 1 2 6b 2 2 2b 2 2 1b 2 2 1a 1 2 Energy · · · Pyrazolide Molecular Orbitals Photodetachment Experiment

4. Negative Ion Photoelectron Spectrometer Energy Analyzer E x B Mass Filter I(KE) e-e- Microwave Discharge Ion Source UV laser 351 nm Acceleration Faraday Cup

5. Detachment from HOMO 1a 2 2 2b 1 2 6b 2 2 2b 2 2 1b 2 2 1a 1 2 Energy · · · Molecular Orbitals

6. Detachment from HOMO  1 1a 2 1 2b 1 2 6b 2 2 2b 2 2 1b 2 2 1a 1 2 Energy · · · X 2 A 2 ~

7. Detachment from HOMO  2 1a 2 2 2b 1 1 6b 2 2 2b 2 2 1b 2 2 1a 1 2 Energy · · · A 2 B 1 ~

8. 1a 2 2 2b 1 2 6b 2 1 2b 2 2 1b 2 2 1a 1 2 Energy · · · B 2 ~

9. Negative Ion Photoelectron Spectroscopy A AB ~ X AB  ~ X AB ~ T0T0 EA (AB) Electron Affinity ← Electron binding energy (eBE) eBE = h – eKE AB  + h AB + e  (eKE) h 351 nm Electron kinetic energy (eKE) →

10. Pyrazolide 351 nm Photoelectron Spectrum

12. Angular Distributions -0.24 -0.65 -0.43 -0.32 -0.46 -0.21  -electron detachment  -electron detachment   

13. Vibrational Modes  C 2v molecule with 8 atoms  18 Vibrational Modes  7 a 1 modes  2 a 2 modes  3 b 1 modes  6 b 2 modes

14. Vibrational Modes  C 2v molecule with 8 atoms  18 Vibrational Modes  7 a 1 modes  2 a 2 modes  3 b 1 modes  6 b 2 modes Independent Harmonic Oscillators with Duschinsky Rotation Geometries and Frequencies B3LYP/6-311++G(d,p)

15. Franck-Condon Simulation of a 2 detachment 2 A 2 10 meV convolution Some features are missing — what about b 2 detachment?

16. Franck-Condon Simulation of b 1 detachment 2 B 1 10 meV convolution Still inadequate — need both states

17. 2-State Franck-Condon Simulation ? 2 A 2 2 B 1 10 meV convolution Need to consider interstate coupling

18. Interstate Coupling 2A22A2 2B12B1

19. Vibrational Modes  C 2v molecule with 8 atoms  18 Vibrational Modes  7 a 1 modes  2 a 2 modes  3 b 1 modes  6 b 2 modes

20. Linear Vibronic Coupling Model Hamiltonian

21. Vertical energy differences Potential energy surface gradients at reference geometry Potential energy surface force constants at reference geometry Interstate coupling constant How are these parameters evaluated? Model Parameters

22. CCSD ab initio calculations  Geometry optimization for anion  Harmonic frequency calculation for anion  Gradients & second derivatives for neutral states at anion geometry  &  Alternatively, optimize neutral geometries and harmonic frequencies  Interstate coupling constants What are the values for these parameters?

23. Gradients, Coupling Constants, and Vertical Energies 0.05 eV — 0.25 eV 0.02 eV — 0.17 eV 0.06 eV — 0.17 eV 0.02 eV How does the simulation appear?

24. Model Potential Simulation a 2 vibronic symmetry b 1 vibronic symmetry 10 meV convolution b2b2 b2b2

25. Pyrazolyl Summary  EA = 2.937 ± 0.006 eV  T 0 = 0.032 ± 0.003 eV  X 2 A 2  a 1 - 1320 ± 65 cm -1  N-N stretch  b 2 - 545 ± 100 cm -1  In-plane distortion  A 2 B 1  a 1 - 755 ± 20 cm -1  N-N stretch  b 2 - 435 ± 50 cm -1  In-plane distortion ~ ~ Non-totally symmetric b 2 modes appear in the spectrum due to vibronic coupling between A 2 and B 1 electronic states

26. Acknowledgements Thanks for your attention Funded by AFOSR NSF