Extremely slow intramolecular vibrational redistribution: Direct observation by time-resolved raman spectroscopy in trifluoropropyne.

We have studied the dynamics of intramolecular vibrational redistribution (IVR) from the initially excited mode v ≈ 3330 cm (acetylene-type H-C bond) in H-C≡C-CF molecules in the gaseous phase by means of anti-Stokes spontaneous Raman scattering. The time constant of this process is estimated as 2.3 ns-this is the slowest IVR time reported so far for the room-temperature gases. It is suggested that so long IVR time with respect to the other propyne derivatives can be explained by a larger defect, in this case, of the Fermi resonance of v with v + 2v-the most probable doorway state leading to IVR from v to the bath of all vibrational-rotational states with the close energies. In addition, it is shown that the observed dynamics is in agreement with a theoretical model assuming strong vibrational-rotational mixing. [ABSTRACT FROM AUTHOR]