1. Photo physics and photo chemistry of ice films on graphite Department of Applied Physics Chalmers and Göteborg University Dinko Chakarov Johan Bergeld Michael Gleeson Bengt Kasemo ……………

2. Key words: Photon induced processes (UV - visible – IR) Water ice (amorphous, crystalline, reactions) Surfaces Graphite Spectroscopy

3. Experimental conditions: ° Atomically clean and ordered surfaces Ice (H2O/D2O) on HOPG (XYA) ° UHV (below 10 -10 torr) ° Temperature range 25 - 1500 K ° Photon fluxes (cw and pulsed) 10 12 - 10 29 photons.s -1 ° Arc lamps + filters/monochromator and/or Nd:YAG based OPO (220-1600 nm) Experimental methods: ° HREELS ° TDS/ITS ° PID ° QCM

4. Ice - Optical / Electronic properties

5. Graphite: Electronic/Optical Properties electronic configuration: 2-4 or 1s 2 2s 2 2p 2 Photon Energy (eV) Extinction coefficient

6. J. Chem. Phys. 106 (3), 982, 1997 PHOTO DESORPTION OF ALKALI ATOMS Graphite

7. Phenomena/Examples: Photoinduced structural changes in amorphous ice Photoejection of water molecules from amorphous ice Photoreactions: H 2 O & coadsorbates on graphite

8. HREELS; energetics orientation ITD; structre coverages TPD; binding energy lateral interactions (UHV and Low Temperatures)

9. Structure of Ice (I c and I h) Hydrogen bonding: Ideal ice structures obey the so-called Bernal-Fowler rules: each hydrogen atom (or proton) is situated on the line joining each pair of oxygens; each oxygen atom has two hydrogen atoms attached to it at distances of about 1Å, thereby forming a water molecule H 2 O.

10. Photoinduced crystallization Experimental observations

11. Re-crystallization Mechanism PRL, 81, 5181 (1999)

12. Defects annealing

13. Structural changes of ice films

14. Importance and Consequences Balance between adsorbed and gas phase water Reactivity of the ice surface

18. Photoreactions with ice; investigated systems: Substrates: Graphite, Si(001), Pt(111), … Coadsorbates: Metal ions and clusters: Na, K, Cs, Ag, Au Simple molecules: CO, NO, H 2 S Observed products: H 2, CO, CO 2, CH 4, NH 3, …

19. AM-stabilized H 2 O : TPD

20. Photoreactions of water and carbon at 90 K J. Chem. Phys. 115 (20) 2001 Carbon/Graphite - C - O - H

21. -250255075100125150175200225 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 Irradiation: 355 nm / 5.3 mJ (10x10 sec exposures) NO desorption Time (sec) NO exposure ~12 L Ag coverage 0,0 ML 0,3 ML 1,3 ML 2,2 ML Photo-desorption as a function of Ag coverage

23. Summary: Photoinduced structural changes in amorphous ice Photoejection of water molecules from amorphous ice Photoreactions: H 2 O & coadsorbates on graphite Demonstrate the richness of the processes and phenomena; Knowing the conditions is possible to identify the predominant process.