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2 Cary 50 Bio UV-VIS Spectrophotometers (2006)

Ultraviolet spectroscopy is applicable solely to conjugated systems. This is because most organic compounds produce no effect whenever the relatively high-energy radiation that constitutes the ultraviolet (200–400 nm) and visible (400–700 nm) portion of the electromagnetic spectrum are presented. Whenever ultraviolet radiation is used, the energy absorbed by a molecule corresponds to the amount necessary to excite electrons from one molecular orbital to another. Typical organic compounds, which mostly contain s bonds, require much higher wavelengths to become excited than what the range of UV will provide. Only those conjugated systems with a number of p bonds are capable of being promoted to higher energy levels by ultraviolet and visible light.

A sample is placed into a cuvette and the spectrum is recorded by irradiating the sample with ultraviolet light of continuously changing wavelength. When the wavelength of light corresponds to the energy level required to excite an electron to a higher energy level, energy is absorbed. This absorption is detected and plotted on the vertical axis as the absorption while the wavelength of the absorbed light is plotted horizontally.


Links:
http://www.shu.ac.uk/schools/sci/chem/tutorials/molspec/uvvisab1.htm
http://www.sci.sdsu.edu/TFrey/Bio750/UV-VisSpectroscopy.html


Contact Information
Dr. Michael Norton
Marshall University Dept. of Chemistry
norton@marshall.edu
304-696-6627

Dr. William Price
Marshall University Dept. of Chemistry
pricew@marshall.edu
304-696-3156