C566lecture28_000 - C566 Master Lecture Notes Lecture 28...

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1 C566 Master Lecture Notes Lecture 28 Diffuse Spectra- Frequently, individual ro-vibronic lines are NOT resolved, and it could be for a variety of reasons. a. Large molecules have small rotational constants and overlapping vibronic bands . Many vibratinoal modes contribute, have comparable vibrational frequencies. b. Lifetime of the excited state may be too short to resolve spacings between rovibronic lines c k k c rad non rad rad non rad 2 1 1 2 1 ~ Quantum yield for fluorescence from S 1 = rad non rad rad f k k k absorbed photons g fluorescin # # Collision free lifetimes of vibrational levels about 5 microsec, drops as E vib increases because of vibrational rotation coupling. Collisions, interactions with matrix, surface or solvent. c. Pseudo-continua. Zero point of S 1 accidentally degenerate with a high rovibrational levels of S 0 and or T 1 , so intersystem corssing is possible. See Jablonski diagram http://www.olympusmicro.com/primer/java/jablonski/jabintro/index.html
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Intersystem crossing is often associated with interactions between chromophore and solvent. Solvent effects on Electronic Spectra Interactions between solvent and solute can either stabilize or destabilize the electronic structure of the solute. Example n- * transition (like formaldehyde) i Non-bonding electron stabilized by H-bonding or dielectric effects of solvent f e - reorganizes FASTER than the solvent, so the f is destabilized relative to i . f
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This note was uploaded on 01/18/2012 for the course C 566 taught by Professor Carolinechickjarroll during the Spring '11 term at Indiana.

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C566lecture28_000 - C566 Master Lecture Notes Lecture 28...

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