Temperature behavior of collisional parameters of oxygen fine-structure lines: O2-O2 case

Abstract

The microwave spectrum of oxygen, which consists of the fine-structure lines, is a tool for atmospheric research. An accurate line shape profile is necessary for modeling of the atmospheric absorption and interpreting the radiometric data. In this study, more than 500 recordings of the oxygen millimeter wave lines were obtained in a wide range of pressures (0.3–1500 Torr) and temperatures (235–357 K) using two experimental techniques that differ in principle of operation. High quality of the experimental spectra and negligible baseline allowed accurate analysis of the line shape using the quadratic speed-dependent Voigt profile. Line shape parameters for six fine-structure oxygen lines (N = 1+,1−, 7+, 11+, 15+, and 19−), including self-broadening and self-shifting, were refined. The parameters of the speed dependence of the collision relaxation rate demonstrated significantly different temperature behavior for different rotational states. In particular, the ratio γ2/γ0 reveals temperature independence for the lowest rotational state; the dependence becomes notable with the growth of rotational excitation. For practical use, the empirical functions were fitted to the experimental temperature and rotational dependences of the line shape parameters.