Knowledge Bank

The high resolution spectra of the fundamental and first overtone of the acetylenic CH stretch in $SF5CCH$ have been measured in a collimated molecular beam. The fundamental spectrum ($\rho A1=191/cm-1$) is only slightly perturbed at low J, K corresponding to an ``effective” lifetime of 2 nsec. Four other weak bands are present in this region and their origin is hypothesized as being due to isotopes and near resonant perturbing states. In the spectrum of the first overtone ($\rho A1=1\times 105/cm-1$), the features have a Lorentzian lineshape and from their average width an intramolecular vibrational relaxation (IVR) lifetime of 1.5 nsec is calculated. The long lifetimes of both bands can be explained by the lack of low order anharmonic resonances.