34_580ln_fa08 - MIT OpenCourseWare http/ocw.mit.edu 5.80...

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MIT OpenCourseWare http://ocw.mit.edu 5.80 Small-Molecule Spectroscopy and Dynamics Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.80 Lecture #3 4 Fall, 2008 Page 1 of 6 pages Lecture #3 4 : Wavepacket Dynamics See pages 626-635 of SDDM for today, pages 635-649 and 659-667 for Wednesday. We mostly do frequency domain spectroscopy, yet we talk about dynamics. But eigenstates are stationary! How are dynamics encoded in a frequency domain spectrum? Today: discuss the famous equivalence: The Franck-Condon distribution in an absorption spectrum is identical to the Fourier transform of the autocorrelation function for a wavepacket created by transferring the initial state from potential surface g (or V ) to surface e (or V ) at t = 0. The autocorrelation function describes the evolution of the g-state wavefunction on the e-state surface, where it is not an eigenstate. The two pictures are mathematically equivalent, but yield quite different sets of insights. Key is that the wavepacket picture is inherently “local” and “ball-and-springs mechanistic”, whereas the traditional frequency domain picture is inherently “global” and quantum mechanical. The stationary phase condition provides the reason why the localized picture emerges and why the autocorrelation function picture gives insights.
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This note was uploaded on 11/28/2011 for the course CHEM 5.74 taught by Professor Robertfield during the Spring '04 term at MIT.

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34_580ln_fa08 - MIT OpenCourseWare http/ocw.mit.edu 5.80...

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