Raman study of the temperature and pressure dependence of vibrational relaxation in propyne

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Abstract
The Raman isotropic band shapes of the ν3 (C≡C stretch) vibration of propyne complexed with acetone have been measured as a function of temperature and pressure. The experimentally determined correlation functions 〈ω(0)ω(t)〉 have been calculated. It is shown that these functions have a long-time tail which is negative. This effect is explained in terms of a slowly relaxing rotational motion which causes the environment of the scattering propyne molecule to change on a time scale comparable to the vibrational relaxation time. The short-time portion of the 〈ω(0)ω(t)〉 function is shown to be dominated by collisional effects. The isotropic band shapes of the ν3 vibration have also been measured for solutions of propyne in inert solvents (tetramethylsilane and carbon disulfide). The analysis of the band shapes suggests that, in these cases, the band broadening is in the ’’motionally narrowed’’ limit.