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Adsorption and self-assembly of glycine nanodeposits on ice nanolayers prepared at low temperature(~125 K) on a polycrystalline copper substrate are studied by means of infrared reflection-absorption spectroscopy (IRAS) under ultra high vacuum conditions. The results show that glycine displays a complex range of adsorption phases that are sensitive to the growth conditions.
At low exposures (E ¡Ü 4 L), the IRAS spectra show evidence that the bonding of glycine to the ice surface is non-dissociative, the bonds being established at the carboxylic group (carbonyl stretch C=O observed at ~ 1720-1740 cm-1). This indicates that the glycine molecules are present on the ice nanolayers in their neutral form with the carbonyl oxygen atom acting as an H-bond acceptor and the acidic hydroxyl group as an H-bond donor.
At exposures E ¡Ý 4 L, the dangling¨C OH found on the ice surface disappears completely.
At high exposures (E ¡Ý 15 L), multilayers build up and the bending mode of the amine group starts growing, leading at higher exposures to a broad asymmetric peak at 1662 cm-1
superimposed on the carbonyl stretch (C=O) at ~ 1720-1740 cm-1.
With the substrate held at temperatures below ~172 K, deprotonation of the glycine molecules leading to proton transfer and consequently to the formation of glycine zwitterions does not occur. For temperatures T >172 K, the desorption of the ice nanolayers starts and a continuous decrease of the carbonyl stretch (C=O) is observed. This means that glycine dissociation occured and this implies that the ice hydrogen-bonded network must be disrupted to transport the hydronium ions. At T= 203 K, the entire ice film has been exhausted and the C=O peak at ~ (1720-1740 cm-1) has totally vanished. The bonding to the Cu surface is through the terminal carboxylate ions (COO-), and glycine is present in its anionic form.
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