Chapter 15 - Chapter 15 Molecular Luminescence Spectrometry...

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Chapter 15 Molecular Luminescence Spectrometry Three types of Luminescence methods are: (i) molecular fluorescence (ii) phosphorescence (iii) chemiluminescence In each, molecules of the analyte are excited to give a species whose emission spectrum provides information for qualitative or quantitative analysis. The methods are known collectively as molecular luminescence procedures.
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Fluorescence: absorption of photon, short-lived excited state (singlet), emission of photon. Phosphorescence: absorption of photon, long- lived excited state (triplet), emission of photon. Chemiluminescence: no excitation source chemical reaction provides energy to excite molecule, emission of photon. Luminescence: High sensitivity strong signal against a dark background. Used as detectors for HPLC & CE.
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THEORY OF FLUORESCENCE AND PHOSPHORESCENCE Types of Fluorescence: Resonance (emitted λ = excitation λ ; e.g., AF) Stokes shift (emitted λ > excitation λ ; e.g., molecular fluorescence)
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Electron spin and excited states Excited, paired = excited singlet state fluorescence Excited, unpaired = excited triplet state phosphorescence
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Deactivation Process by which an excited molecule returns to the ground state Minimizing lifetime of electronic state is preferred (i.e., the deactivation process with the faster rate constant will predominate) Radiationless Deactivation Without emission of a photon (i.e., without radiation)
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TERMS FROM ENERGY-LEVEL DIAGRAM Term: Absorption Effect: Excite Process: Analyte molecule absorbs photon (very fast ~ 10 -14 – 10 -15 s); electron is promoted to higher energy state. Slightly different wavelength excitation into different vibrational energy levels. Term:
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This note was uploaded on 05/06/2010 for the course CHEM 4414 at Arkansas Tech.

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Chapter 15 - Chapter 15 Molecular Luminescence Spectrometry...

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