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Femtosecond Dynamics in the Photoprotection in Thymine Brian McFarland and the LCLS Nucleobase Photoprotection collaboration. UV Excitation . Photoprotection. X-Ray Probe. Motivation:. Experiment:. p*. Auger. p → p *. n → p. DNA photoprotection. IP. - PowerPoint PPT Presentation
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DNA photoprotection• 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
Experiment:
Results: Future:
AugerMatrix Element:
p
n
IP
O1s
p*UV Excitation Photoprotection
n → p p → p*
X-Ray Probe
X-ra
y pu
lse
Auger
1 2
3
Δt?TimeDelay
baba
corefree r
,
1
Valence and core overlap give site and orbital selectivity
n orbital contributions
Core
Motivation:
ExcitationTu
nabl
e X-
Ray
Prob
e
• Tunable/Selectable Photon Energy: Monochrometer/Seeded FEL. Desired Resolution: < 0.5 eV• Other DNA bases/ Gas phase samples• Liquid samples/environments
Pump ON – Pump OFFPump ON+Pump OFF
Time dependent X-Ray Absorption and Emission Measurements
Time Independent NEXAFS: ALS BL8
Capabilities:Electron Kinetic Energy (eV)
490 500 510 520 530 540
Phot
on E
nerg
y (e
V)
528
530
532
534
536
538
540
Femtosecond Dynamics in the Photoprotection in ThymineBrian McFarland and the LCLS Nucleobase Photoprotection collaboration