Chemists shed light on sun’s role mixing up molecules

University of Sydney scientists have discovered a startling new mechanism where sunlight can rearrange the atoms of molecules to form new chemical substances. The research, by Professor Scott Kable , Dr Meredith Jordan and collaborators at the School of Chemistry , is published in a recent . It has implications for the extent that pollutants are dispersed across the Earth's surface, and how quickly they are removed. Until now, chemical models of the atmosphere assumed a molecule emitted into the atmosphere stays fixed as that molecule, until it is either photolysed (broken up) by sunlight, or attacked by other molecules. Professor Kable and Dr Jordan have now overturned this theory using a common, small pollutant molecule, acetaldehyde, in a lab-based experiment that substituted a laser light for the sun. "We chose a special variant of the acetaldehyde compound, where three of the four hydrogen atoms were replaced with 'heavy hydrogen' (called deuterium)," Professor Kable explains. "While not changing any of the chemical or photochemical properties to any significant extent, this subtle chemical change did allow us to follow the photochemical reactions with much more detail." Professor Kable says conventional atmospheric models predicted that acetaldehyde should simply break in half when it absorbs light.