Propellanes vibrational spectra

The vibrational spectrum of bicydo[1.1.0]butane has been examined but not with the aid of calculated force constants Therefore it would be premature to compare the force constants for cyclopropane and bicyclobutane. A complete analysis has been performed for [l.l.l]propellane , but again a re-examination of bicyclobutane is needed in order to make meaningful comparisons. 

An unresolved puzzle remains22 the first two vibrational peaks in the first band in the photoelectron spectrum are separated only by 360 20 cm4, less than the lowest frequency vibration observed in neutral propellane (529 cm4), and very much less than its lowest totally symmetric vibration (908 cm 1). Yet, the authors calculations22 suggest that the lowest frequency totally symmetrical vibration of the radical cation will be at higher and not lower frequencies. The authors suggested that the vibrational structure may be due to vibronic mixing with the lowest excited state of the radical cation. 

From infrared and Raman spectra of bicyclobutane and appropriate deuterated isomers a new vibrational assignment was made with the help of the spectrum calculated using the 6-3IG basis set. A normal coordinate analysis furnished atomic polar tensors and related properties. The results were compared with similar data for cyclopropane and [l.l.l]propellane. 

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