Molecular relaxations in mixtures of O2 with CO2 observed on laser-induced gratings

Laser-induced gratings in mixtures of O-2 with CO2 were formed by excitation of the O-2 molecules to the singlet state b (1) I pound (g) (+) (v'=0). Density changes from heat release and from electrostriction, and variation of electric polarizability by excitation of molecules contribute to the grating. For modeling the relaxation of the excited O-2 molecules, a three-step process is assumed: Fast heat release with respect to the rotational states first, then medium fast electronic de-activation with excitation of vibrational states of the O-2 and CO2 molecules, and then the final slow heat release processes. The observed temporal evolution of the diffraction efficiency of the grating agrees rather well with modeling. Average rates of the final relaxations and the value of the polarizability of the singlet state b (1) I pound (g) (+) (v'=0) are determined in this way.