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GRADUATE SEMINARS AFTERNOON

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2:30 Introduction and Easter Term Lowry Prize

2:35 Tej Bhinde “The two-dimensional crystalline structures of alkyl amides adsorbed on the surface of graphite”

The sub-monolayer (2D) structures of alkyl amides adsorbed on graphite using a combination of synchrotron X-ray and neutron diffraction are presented. The calculated structure reveals that these molecules lie flat on the graphite surface. Depending on the number of carbons (odd/even) and length of the alkyl chain, the structure of the adsorbed layer possesses different ‘wallpaper symmetries’. The calculated 2D structure is in reasonable agreement with the structure proposed by microscopy (STM) for a similar amide homologue but with far greater (atomic) resolution. A ‘network’ of hydrogen bonds imparts very high stability to the monolayer, higher than that seen before for similar adsorbed species. Various hydrogen bond properties, such as hydrogen bond lengths and angles, for the different hydrogen bonds present in the system have been calculated.

3:05 Seung Yeon Lee “Thin Water Layer on Charged Surfaces in Oils”

The aim of this work is to investigate the presence of thin water layers on charged surfaces in oils and to address how the water layers change depending upon added salts’ concentrations and valence. In particular we are ultimately concerned with adsorption at clay surfaces, representing one of the largest components of mud and rock and hence with significant importance to the environment. Importantly clay surfaces are often charged to a different degree depending upon the type of clay under consideration. This provides an ideal opportunity to vary the interaction of the substrate with a variety of species, most particularly aqueous solution of ions of different valency. We used an initial method on calcium carbonate particles dispersed in cyclohexane and then, silica particles in heptanes for small angle neutron scattering in order to identify any water layers and measure the thickness. Additional techniques have also been investigated to observe thin water layers at the silica/oil interface, including ellipsometry. Indeed we have observed macroscopic water layers and been undergoing salt concentration and valence

3:35 Alex Ievins “Understanding the Metal-Organic Interface”

Much attention has been given to the interaction of organic molecules at metal surfaces in recent years, notably within the context of heterogeneous catalysis. Of specific interest is the observation of a range of locally and globally organized chiral structures, on both intrinsically achiral and chiral substrates. We have shown that chiral fcc surfaces have a high surface energy and necessarily contain low-coordinated kink sites, which cause the surface to deviate significantly from the ideal structure. In contrast, bcc surfaces may be chiral and stepped only, without the presence of kinks.

A bi-metallic system of bcc copper grown on iron is first introduced as a model substrate to exploit the novel symmetry properties of the bcc structure, whilst retaining the capability for non-dissociative adsorption of organic molecules. Monte Carlo simulations are then used to demonstrate the enhanced stability of the bcc system with respect to thermal roughening. Finally we show that molecular dynamics simulations provide an improvement upon static calculations, by giving a more realistic and visible description of molecular vibration and conformational freedom at finite temperature.

4:05 Tea & Coffee in Foyer

4:35 Ailsa.K. Benton (Supervisor: Prof. R. L. Jones) “Studies of night-time nitrate chemistry in the urban boundary layer using LED -BBCEAS”

Cavity-enhanced absorption spectroscopy enables the unambiguous determination, in both laboratory and field atmospheric studies, of the concentration of gases at ppt-ppb levels. This method has been applied to the measurement of concentrations of NO3 and N2O5 during the Regent’s Park and Tower campaign at a height of 185m above central London. NO3 is rapidly photolysed in the day but is the primary night-time oxidiser of VOCs, and through its equilibrium with N2O5 is an important source of the HNO3 reservoir, which, on removal by dry or wet deposition, influences NOx and hence O3 budgets. A large vertical gradient in NO3 and N2O5 is expected in the nocturnal boundary layer, due to the variation in proximity to sources and sinks. However, due to the inherent difficulties in making measurements above cities, there are very few measurements between ~50 and 300m above the ground. I will discuss one such campaign, and how my results, in conjunction with ancillary data, compare with global and box-model studies. Implications for our ability to describe the oxidative ability of the atmosphere will also be discussed.

5:05 Luke Knowles “Atmosphere – Biosphere Interactions modeling surface deposition”

5:35 Refreshments will be served in the Todd Hamied Room for all attendees AFTER the Graduate Seminars

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