vibrational sum rule

vibrational sum rule

[vī′brā·shən·əl ′səm ‚rül]
(spectroscopy)
The rule that the sums of the band strengths of all emission bands with the same upper state is proportional to the number of molecules in the upper state, where the band strength is the emission intensity divided by the fourth power of the frequency.
The sums of the band strengths of all absorption bands with the same lower state is proportional to the number of molecules in the lower state, where the band strength is the absorption intensity divided by the frequency.
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