Assumptions about how certain key molecules behave on the surface of dust grains in deepest space might be wrong, report UK chemists.   

Research by Wendy Brown at University College London's chemistry department explores the chemical reactions that occur on the surface of interstellar dust. The dust grains are believed to be largely carbon- and silicon-based, and are often covered in films of frozen water and other molecules such as methanol and carbon dioxide. 

Brown's team is simulating the conditions of deep space in the laboratory and using graphite surfaces as model dust grains. Her team has been gathering the most detailed data yet on the kinetics of desorption of key small molecules from graphite. 

'The current models for this process, based on experiments with metal surfaces, assume that all these key molecules come off the particles with a perfect zero-order desorption,' said Brown. 'A given molecule on the surface is "unaware" of its neighbours. As soon as the correct temperature is reached, all the molecules explode off the surface simultaneously regardless of the initial concentration.' 

But the UCL team has shown that for graphite surfaces this is not the case. 

'We have measured the kinetics of desorption of methanol, water and ammonia from graphite. Our earlier work showed that methanol has a desorption order of 0.35; new work has shown that both water and ammonia have a desorption order of 0.25.' 

Brown is not sure if this will affect astronomical models. 'It is conceivable that the new kinetic data might be significant for regions adjacent to some types of stars and not others,' she told Chemistry World.   

'But in any event it is important that the role played by the dust surfaces is fully understood. It might be that the nature of the surface is irrelevant, or else it could be important. Either way, the astronomers need to know.'   

Simon Hadlington