Credit: Greg Stewart/SLAC National Accelerator Laboratory
Thymine – the molecule illustrated in the foreground – is one of the four basic building blocks that make up the double helix of DNA. It’s such a strong absorber of ultraviolet light that the UV in sunlight should deactivate it, yet this does not happen. Researchers used an X-ray laser at SLAC National Accelerator Laboratory to observe the infinitesimal leap of a single electron that sets off a protective response in thymine molecules, allowing them to shake off UV damage.