Animation of an ethanol molecule in a beam of infrared light. Ethanol is the alcohol found in drinks. The way it behaves under infrared (IR) light is characteristic of the molecule, and this behaviour has been used in tests for alcohol in people, such as in the breathalysers used to determine alcohol consumption by suspected drink drivers. Under infrared light, some of the bonds linking the atoms are excited (red), and they absorb specific wavelengths of the IR energy, which makes them stretch more vigorously than usual. Each type of bond absorbs a particular wavelength, and the resulting absorption spectrum can be used to identify the molecule in a sample. See clip K003/7355 for a diagram of the infrared spectrum of ethanol, and the bonds responsible for its appearance.