The development of a sophisticated model is presented for fitting the experimental Raman spectra of liquid acetonitrile. A new approach for extracting all possible band shape details of highly overlapping spectral bands is derived and implemented. A unique, statistically justifed resolution is obtained of the v2 vibrational band into its components at 25, 50 and 75°C. The parameters of both the real and imaginary parts of the vibrational correlation functions are reported for the first time together with their confidence intervals. The quantitative characteristics obtained of the v2 mode dynamics can be considered as experimental data and used for testing theoretical models of vibrational relaxation.