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

Abstract

Laser-induced gratings in mixtures of O₂ with CO₂ were formed by excitation of the O₂ molecules to the singlet state b ¹ Σ ⁺ _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 O₂ 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 O₂ 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 Σ ⁺ _g (v′=0) are determined in this way.