UV-Vis - UV/Vis (Ultraviolet and Visible) Spectroscopy...

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Unformatted text preview: UV/Vis (Ultraviolet and Visible) Spectroscopy Agilent 8453 Diode Array UV-Vis Spectrophotometer Varian Cary 5000 UV-Vis-NIR Spectrophotometer Wavelength and Spectroscopy What Do We Observe = 200 ~ 700 nm UV/Vis spectroscopy is used to detect the presence of certain functional groups called chromophores , especially in conjugate systemssuch as aromatics, dienes, polyenes, and , -unsaturated ketones Absorption of UV or visible light occurs only when the energy of incident radiation is the same as that of an electronic transition in the molecule. Electronic excitation Instrument (double beam) Typical = 200 ~ 700 nm Instrument (Diode Array) Rugged, fast, and reliable Solvents and Cuvettes for UV/Vis Spectroscopy The Beers Law A = log ( ) I ref I sample I ref I sample > 1, thus A is aways positive. I ref I sample = 1 A = 0 I ref I sample = 10 A = 1 I ref I sample = 100 A = 2 I ref I sample = 1000 A = 3 A = x c x l : molar absorptivity constant or extinction coefficient (l mol-1 cm-1 ) c : concentration (mol/l) l : path length (cm) Typical UV/Vis Spectra O CH 3 Franck-Condon Principle Nuclear motion is negligible during the time required for an electronic transition. Excitation can occur from the ground state to any of the excited state vibrational levels....
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UV-Vis - UV/Vis (Ultraviolet and Visible) Spectroscopy...

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