Continuum absorption in pure N2 gas and in its mixture with Ar

Abstract

The N${}_2-$N${}_2$  and N${}_2-$Ar continuum absorption spectra are calculated using the classical trajectory-based simulation (CTS). The spectra obtained are validated by new measurements in the subTHz spectral range along with the previously reported data in the far infrared. A novelty of our approach consists in the use of the CTS method to simulate both the fundamental nitrogen absorption band and the rototranslational band in N${}_2-$Ar , i.e., we succeeded to step beyond the conventionally used approximation of the only rigid monomers. This extension of the theory made it possible, in particular, to demonstrate the validity of the rigid monomer assumption for the CTS simulation of the rototranslational N${}_2-$Ar band. The broadband spectra within 77–354 GHz were measured using the resonator spectrometer at temperatures of 278–333 K and pressures of 900–1600 Torr. A minor underestimation of the calculated absorption by 3.7% and 5% is shown for the N${}_2-$N${}_2$  and N${}_2-$Ar system, respectively. On the basis of the obtained data, a new analytical model is developed for the N${}_2-$N${}_2$  absorption in the subTHz range, which can be used in radiation propagation codes for the Earth, Titan, or other nitrogen-rich atmospheres. The advantage of the model proposed here over those previously published is discussed.