Using a new version of the Talbot-Rayleigh method we recorded the I (lambda) channeled spectra of uniaxial nematic liquid crystal at different temperatures. We derive the theoretical expression of I (lambda) that involves a three-band model for the refractive indices, which is then, fitted with the experimental data by a nonlinear optimization procedure. As a result, we compute the dispersion curves n(o), n(e), Deltan, their temperature dependencies, and the band contributions.