Optical scattering from laser-induced thermal gratings (LITGs) was employed in investigations of molecular relaxation processes in gas mixtures containing a small amount of NO2 diluted with different buffer gases (N-2,Ar, CO2). The thermal gratings were generated by the thermalization of the molecular internal energy stored in the NO2 molecules after laser resonant excitation of the B-2(I) <-- (2)A(1) Huber-Douglas band. The temporal evolution of LITGs was detected by scattering a cw read-out laser beam. A theoretical simulation of experimental results was performed in which the linearized hydrodynamic equations relevant to collisions responsible for the relaxation process were solved by following a two-step rate equations approach.