1 Femtosecond Time and Angle-Resolved Photoelectron Spectroscopy of Aqueous Solutions Toshinori Suzuki Kyoto University photoelectron

Electron dynamics in water Electron dynamics in water Pure water H-Bond Network ・ Elucidation of Hydration around solutes ・ Chemical Reaction ・ Real-time dynamics Quantum Chemistry, MD Simulation Change of H-bonding Biomolecule & Water Water and Hydration Energy Conversion Energy Conversion Life Innovation Green Innovation

Photoelectric effect 3 Kinetic Energy = h – eBE eBE: electron binding energy Sample

4 Example: Charge Transfer from DABCO to Water 0.1M DABCO hv probe 260nm (4.77eV) hv pump 226nm 0 eBE S2S2 electron kinetic energy tt hydrated electron vacuum level S0S0 Time-Resolved Photoelectron Spectroscopy of Aqueous Solutions

5 e-e- liquid beam detector flight tube ~ 1m femtosecond laser pulses Magnet e-e- TOF e - energy analyzer liq. N 2 trap nozzle detector Time-Resolved Photoelectron Spectroscopy of Aqueous Solutions Torr Torr 50% collection efficiency  0.5 mm aperture TMP

6 Example: Charge Transfer from DABCO to Water 0.1M DABCO hv probe 260nm (4.77eV) hv pump 226nm 0 eBE S2S2 electron kinetic energy 3.4 eV: Signature of hydrated electron tt hydrated electron vacuum level S0S0

Electronic transitions of hydrated DABCO has characters of charge transfer to solvent 7 S1S1 S 2, S 3, S 4 Yamamoto et al., Phys. Rev. Lett. 112, (2014) p Rydberg s Rydberg CAM-B3LYP/6-311G++ 300K equiliburaium 2nm radiua classical sphere

8 Angle-Resolved Measurement Rotating detection axis or Rotating polarization axis This Work

9 Time and Angle-Resolved Measurement Low collection efficiency probe analyzer 100 kHz laser Rotating polarization No magnet str detection solid angle Phys. Rev. Lett. 112, (2014) 1°  40 mm 1.2m

100 fs 200 fs 300 fs 3 ps (hydrated electron) Angle-resolved experiment: 4 selected time delays

11 Polarization dependence of photoelectron Aqueous DABCO solution eBE (eV) S(E,  ) (arb. units) e-e- probe pump detection 100 fs anisotropic Strong photoemission parallel to the probe laser polarization at low eBE parallel vertical

12 eBE (eV) S(E,  ) (arb. units) Time evolution  t = 100 fs  t = 200 fs  t = 300 fs  t = 3 ps anisotropic parallel vertical hydrated electron Phys. Rev. Lett. 112, (2014)

Elastic and inelastic scattering reduces photoemission anisotropy e-e- species at the surfacespecies in the bulk 2~5 nm probing depth e-e- anisotropy is reduced by elastic scattering by water. e-e- anisotropy is observed

14 DABCO is segregated on liquid surface Probing depth is limited. hydrophobic eBE  (eV) Photoelectron signals  (arb. units) N1s 5 1 NH 4 + is not surface active. Gopalakirishnan et al., J. Phys. Chem. B, 109, 8861 (2005) DABCO has an enhanced molecular density on the liquid surface. More signalLess signal Soft X-ray photoelectron spectrum

Our electron scattering calculations on DABCO with 64 water molecules predicts isotropic photoemission  DABCO should be on the liquid surface 15 Phys. Rev. Lett. 112, (2014) anisotropy isotropic anisotropic

16 CTTS reaction occurs to the bulk side probe laser polarization e-e- e - aq e-e- CTTS reaction

Summary The first time- and angle-resolved photoelectron spectroscopy of aqueous solutions has been demonstrated. Photoemission was anisotropic from chemical species near the surface. No evidence was found for an electron trapped on liquid water surface.

Coworkers & Funding Yo-Ichi Yamamoto Yoshi-Ichi Suzuki Shutaro KarashimaTakuya Horio Gaia Tomasello (Wurzburg) Roland Mitric (Wurzburg) JST-CREST