Raman study of vibrational relaxation of 1-alcynes in solution v(≡CH) and v(C≡C) modes of 1-hexyne and 1-decyne

Abstract

The I.R. and Raman bandwidths of the v(≡C-H) and v(C≡C) stretching modes of 1-hexyne and 1-decyne have been measured in dilute solutions in n C₇H₁₆ and CCl₄ as a function of temperature. The I.R. spectrum is used, by comparison with the Raman spectrum, to verify the generally assumed absence of correlation between the rotational and vibrational relaxations. The important experimental findings is the opposite effect of temperature on the isotropic Raman linewidths of the two modes. The v(≡C-H) mode broadens with decreasing temperature and this is interpreted in a qualitative way by the isolated binary collision model of Fisher and Laubereau and the hydrodynamic model of Oxtoby. On the contrary, these models are unable to interpret the linewidth of the v(C≡C) mode. A possible explanation lies in an intramolecular energy relaxation between Fermi resonance levels. Finally, application of the Kubo stochastic line shape theory to the vibrational correlation function of the v(≡C-H) mode shows that the modulation is fast in n C₇H₁₆ specially at high temperature and intermediate between fast and slow limits in CCl₄.