1. Pump-Probe Photoionization & Mass Spectroscopy of Pentamethylcyclopentadiene Fedor Rudakov Peter Weber Molecular Spectroscopy June 21, 2007

2. CONCLUSIONS:   The 2 1 A 1 state is reached with a time constant of 55 fs...  .... Decays with a 84 fs time constant Kuthirummal, Rudakov, Evans, and Weber, J. Chem. Phys. 125, 133307 (2006). Recent Work on 1,3-cyclohexadiene

3. 267nm Pentamethyl Cyclopentadiene e-e- 400nm 1B 2 2A 1 1A 1 Ry

4. Experimental setup CPU Timing Electronics Regenerative Amplification Laser System Ion MCPs e - MCPs 3ω3ω 2ω2ω BBO upconversion Molecular beam Time Delay Stage

5. Pentamethyl Cyclopentadiene Time-Resolved Time-delayed experiments: Pump: 267 nm pulse Pump: 267 nm pulse Probe: 1 or 2 photons of 400 nm Probe: 1 or 2 photons of 400 nmSignals: Mass spectra Mass spectra Photoelectron spectra Photoelectron spectra 2A 1 267nm e-e- 400nm 1B 2 Time Delay 1A 1 400nm

6. Time-resolved mass spectrum  As the wave packet evolves on the electronic surfaces, energy is deposited in vibrational coordinates.  Once ionized, this energy may suffice to fragment the molecule on the way to the mass spec detector.  The early decay of the parent mass reflects the loss of electronic energy as the wave packet moves out of the 1B 2 state (165 fs).  The fragments show an initial rise (165 fs) when the molecule crosses from 1B 2 to 2A 1. The decay of the fragment peak shows the curve crossing through the lower conical intersection (101 fs). All Fragments Combined Parent Mass x10 Xe-Instrument function FWHM=163(7)

7. Time-Resolved Mass Spectrum  As the wave packet evolves on the electronic surfaces, energy is deposited in vibrational coordinates.  Once ionized, this energy may suffice to fragment the molecule on the way to the mass spec detector.  The early decay of the parent mass reflects the loss of electronic energy as the wave packet moves out of the 1B 2 state (165 fs).  The fragments show an initial rise (165 fs) when the molecule crosses from 1B 2 to 2A 1. The decay of the 2A 1 state is seen by the decay of the fragment signal (101 fs). All Fragments Combined ParentMass 267nm e-e- 1B 2 2A 1 Time Delay 1A 1 400nm

8. Time-resolved photoelectron spectra 267nm e-e- 400nm 1B 2 0 fs 200fs 2 ps 1A 1 2A 1

9. Mass and Photoelectron spectra All Fragments Combined Parent Mass 2A 1 State 1B 2 State

10. Summary: Curve Crossing Dynamics in Pentamethyl Cyclopentadiene  We watched the transition from the 1B 2 state to the 2A 1 state …  … before transition to the ground state 1A 1 We observed molecule in 1 B 2, the 2 A 1 and the 1 A 1 state by photoelectron and mass spectroscopy 2A 1 We learned: Energetics:  The ionization energy is at 7.30 eV Dynamics:  It takes 165 fs to leave the 1 B 2 state  The life time of the 2 A 1 state is 101 fs No structural changes take place on the ground State 267nm 165 fs 101 fs 1B 2Fast 1A 1

11. Acknowledgements Job Cardoza Mike Minitti Narayanan Kuthirummal Joe Bush Xinli Yang Funding: DOE