Collisional relaxation and internal energy redistribution in NO2 investigated by means of laser-induced thermal grating technique

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 (N2,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 2B1←2A1 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.