The energy levels of electrons in atoms and molecules are quantised, and the absorption and emission of electromagnetic radiation only occurs at specific wavelengths. In this way, most of the fluorescence signal, which is not as strongly wavelength-dependent, can be eliminated. The Photoacoustic measures the sound waves produced upon the absorption of radiation. Ultraviolet (UV) and visible (VIS) spectroscopy. This is the earliest method of molecular spectroscopy. A phenomenon of interaction of molecular with ultraviolet and visible lights. Absorption of photon result in electronic transition of a molecule, and electrons are promoted from ground state to higher electronic states.
