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Photo-chemistry of caged molecules

Water is one of the most intriguing substances in the universe. It exists almost everywhere from interstellar space to the depth of our oceans. They exhibit interesting physical and chemical properties. Over solid surfaces water grows as Amorphous Solid Water (ASW), having unique properties that we plan to explore.

            One interesting feature is the caging phenomenon. If we adsorb molecules upon a surface and then further adsorb water molecules, the later will substitute the parent molecules at the binding sites on the surface. If the amount of water molecules is large enough (coverage > 10ML) the parent molecules will be concentrated as a micelle-like cage at a point inside the bulk of the thin ASW film. Photochemistry of caged molecules displays different chemical and physical properties than surface photochemistry. The model that describes these reactions is the Dissociative Electron Attachment (DEA). Usually, the substrate-electrons are pumped onto the adsorbent, in the case of ASW; the later stabilizes these hot electrons.

            ASW has the ability, not only to stabilize photo induced electrons, but also positive ions. If the ion deposition takes place on the ASW-vacuum interface a capacitor-like thin film is produced: A nano-capacitor. The inner electric field that develops is of high magnitude due to the small distance between the substrate acting as the first electrode and the surface of the ASW, acting as the counter electrode.   

            In this research I shall investigate the photochemistry of trapped, caged molecules initiated by hot electrons under the influence of electric field induced by the charged ASW nano-capacitor. Charging the dielectric material from dipolar (water or ammonia) to non-polar (e.g. hexane) novel properties of such nano-capacitor will be explored. In addition, upon embedding semi conducting or metallic films (or quantum dots) within the ASW nano-capacitor new photochemical pathways will be revealed.  

 

 

 

 

 

 

 

 

 

Left: CD₃Cl/H₂O coadsorption system. The CD₃Cl layer is initially compressed into 3D islands. The methyl chloride molecules are eventually encapsulated and caged within the water hydrogen-bonded network. Right: The voltage measured right after the “soft sputter” as a function of ASW multilayer thickness (1ML=3.6Å). The initial charge is calculated from the initial voltage and thickness. Right: