The premelting of ice studied with photoelectron spectroscopy

We address the century-old puzzle of the existence of a liquid-like layer at the ice surface near its melting point with new photoelectron spectroscopic tools using synchrotron radiation. Near-edge x-ray absorption shows that a liquid-like film exists at temperatures as low as -20degreesC. Near 0degreesC this film is about 20 Angstrom thick, i.e., six bilayers. With high-pressure x-ray photoelectron spectroscopy, we have further investigated the effect of surface contamination, which is ubiquitous in natural environments, on the state of the ice. Our results show that the premelting of ice can be strongly enhanced by the presence of hydrocarbon contamination.