Ultraviolet Photoelectron Spectroscopy (UV-PES): This is a form of spectroscopy which measures the kinetic energy of electrons emitted from a sample when it is irradiated with high energy ultraviolet radiation.

Unit Cell: The basic component which, when repeated periodically, makes up the overall structure.

Unsaturated: Compare with saturated. A carbon chain is unsaturated if it contains multiple (carbon-carbon) bonds.