Sum-over-states model

The first term in the brackets is the expectation value of the square of the dipole moment operator (i.e. the second moment) and the second term is the square of the expectation value of the dipole moment operator. This expression defines the sum over states model. A subjective choice of the average excitation energy As has to be made. 

What is remarkable is that all of these early measurements of the UV resonance Raman spectra of nucleic acid components involved computational and theoretical support to their experimental findings. For example, Spiro used CINDO calculations to determine the nature of the excited electronic states of the nucleotides [157], In the early and mid 1970 s, many researchers were also attempting to understand resonance Raman spectroscopy, the types of information it could provide, and a unifying theoretical framework to the intensities [147, 159-172], UV resonance Raman spectra provided some of the first experimental evidence to test the various theoretical models. Peticolas attempted to fit the observed experimental excitation profiles of AMP [156], UMP [151, 154] and CMP [152, 153] to the sum-over-states model for the resonance Raman cross-sections. From these simulations, they were able to obtain preliminary excited-state structural dynamics of the nucleobase chromophores of the nucleotides for UMP [151, 153, 158] and CMP [153], For AMP, the experimental excitation profiles were simulated with an A-term expression, but the excited-state structural changes were not obtained. Rather, the goal of that work was to identify the electronic transitions within the lowest-energy absorption band of adenine [156],... 

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See also in sourсe #XX -- [ ]

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