1. Femtosecond Dynamics in the Photoprotection in Thymine
Brian McFarland and the LCLS Nucleobase Photoprotection collaboration
Motivation:
Experiment:
DNA photoprotection
Auger
Matrix Element: p n IP
O1s p*
UV Excitation
Photoprotection
n → p
p → p*
X-Ray Probe
X-ray pulse 1 2 3
Δt?
Time
Delay
Valence and core overlap give site and orbital selectivity
Strong absorption in the UV
Photo excited states reactive:
How does the molecule survive?
Predicted non-Born-Oppenheimer
relaxation: 100 fs? Several ps?
New approach gives spatial/orbital
sensitivity
Results:
Future:
n orbital
contributions
Time dependent X-Ray Absorption and Emission Measurements
Pump ON – Pump OFF
Pump ON+Pump OFF
Time Independent NEXAFS: ALS BL8
528
530
532
534
536
538
540
Excitation
Tunable X-Ray Probe
Photon Energy (eV)
Core
Electron Kinetic Energy (eV)
Capabilities:
Tunable/Selectable Photon Energy: Monochrometer/Seeded FEL.
Desired Resolution: < 0.5 eV
Other DNA bases/ Gas phase samples
Liquid samples/environments