Vibrationally unredistributed emission

Estimates of IVR rates have also been inferred from spectral studies. The principal spectral approach, the measurement of the emission spectra of isolated molecules (for a review, see, for example, Ref. 3), relies on the fact that the spectral characteristics of emission from a molecule will depend intimately on the vibrational character of the excited molecular state. If one prepares a gaseous molecule in a well-defined vibrational state and subsequently observes emission bands that would not be expected to arise from this initially prepared state, then some IVR process can be inferred. Moreover, a rate can be calculated for the process by comparing the intensities of expected emission bands (vibrationally unredistributed emission) and unexpected emission bands (vibrationally redistributed emission). Redistributed and unredistributed emission often are loosely termed relaxed and unrelaxed. Since energy is conserved in isolated molecules, there is no real energy relaxation, as occurs in solution or in solids. 

Equation (2.3) is the key result for the use of spectral information to obtain quantitative information concerning IVR. By determining experimentally the ratio of vibrationally redistributed (Iab>) to vibrationally unredistributed (/ .,) emission, together with knowledge of kf, one can obtain kIVR. kIVR, in turn, can provide other information about the dynamics (within the constraints of the kinetic model). For instance, average vibrational coupling matrix elements can be obtained from a Fermi golden rule expression for the rate. 

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See also in sourсe #XX -- [ ]

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