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C566lecture24_000

C566lecture24_000 - C566 Master Lecture Notes Lecture 24...

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1 C566 Master Lecture Notes Lecture 24 Which vibrational modes are “active” in electronic spectra (active mode = progressions for that vibrational mode are observed in the spectrum) Bottom Line For totally symmetric vibrational modes , in an electronic transition,  = 0, 1, 2, For non-totally symmetric modes ,  = 0, 2, 4, … But, the fact that something is allowed does not mean you’ll see it! Overlap integrals for non-totally symmetric modes are generally very small (there Q for non-totally symmetric modes is ZERO unless the molecule in the different electronic states belongs to different point groups!, so the  = 0 FCF is close to 1, and the  = 2 will be very small), Analysis of Vibrational Structure in S 1 S 0 transitions Assign observed vibronic lines to quantum changes in particular vibrational modes. Learn about vibrational frequencies in S 1 state- back out information about bonding, relate to electronic structure change in S 1 S 0 transition Set up studies of excited state dynamics (how does energy flow in the excited state?) Tools available: Helpful to know vibrational frequencies on the ground state (S 0 ) o Raman spectroscopy o IR Single vibrational level fluorescence Supersonic jets- low temperatures simplify vibrational structure by depopulating excited vibrational levels in  . High-resolution band contours- distinguish between x , y , z , get vibrational symmetry, structural parameters.
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