Question

Explain what is happening at the molecular level during a UV-Vis spectroscopy experiment.

Answer 1

Whenever a photon strikes a molecule, it will be absorbed and the molecule will be promoted from its ground state into a higher energy state (excited state). The energy difference between these two states is known as the bandgap. The energy of the photon should be exactly matched with the band gap in order for the photon to be absorbed. The bandgap is dependent on the structure of the molecule, therefore each molecule has a unique absorbance spectrum.

The absorbance of the molecules follow Beer's Law, which states that absorbance equals the molar attenuation coefficient times the path length and concentration. The molar attenuation coefficient is dependent on the individual compound's ability to absorb light (photon of a particular energy) of a specific wavelength. Beer's law is generally used to calculate concentration of the sample.