Relaxation processes in singlet O-2 analyzed by laser-induced gratings

Thermal laser-induced gratings have been generated in mixtures of oxygen with other gases by the formation of a rotational state thermal equilibrium after the excitation of the O-2 molecules to the singlet b(1)Sigma(g)(+)(nu' = 0) state. The sign and the amount of energy transfer in the formation of the rotational state thermal equilibrium are determined by measuring the phase in the oscillation of the diffraction efficiency of the grating. The values are compared with values, which were calculated assuming a Boltzmann distribution in the rotational states. Furthermore, the effect from the slower vibrational and electronic relaxation processes on the first stage on the grating formation is calculated and compared with the experimental findings. (C) 2000 Elsevier Science B.V. All rights reserved.