Photoacoustic effect a rotating slotted wheel. He noticed that the resulting acoustic signal was dependent on the type of the material and correctly reasoned that the effect was caused by the absorbed light energy, which subsequently heats the sample. Later Bell showed that materials exposed to the non-visible (ultra-violet and infra-red) portions of the solar spectrum can also produce sounds and invented a device, which he called "spectrophone", to apply this effect for spectral identification of materials. Bell himself and later John Tyndall and Wilhelm Röntgen extended these experiments, demonstrating the same effect in liquids and gases. However, the results were too
Ultraviolet photoelectron spectroscopy seen a considerable revival with the increasing availability of synchrotron light sources which provide a wide range of monochromatic photon energies. Ultraviolet photoelectron spectroscopy Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules which have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence region. If Einstein's photoelectric law is applied to a free molecule, the kinetic energy (formula_1) of an emitted photoelectron is given by where "h" is Planck's constant, ν is the frequency of the ionizing light, and I is an ionization energy for the formation