In this work, the auto-correlation function of the center of mass velocity has been used to deduce the mass diffusion coefficient (D) of water diluted in nitrogen using the Classical Molecular Dynamics Simulations (CMDS). The calculations have been performed at room temperature (296 K) for different mixtures of H2O in N2 and 2.107 molecules from a five-sites potential. The results show that the auto-correlation functions expected exponential decay behavior [i.e. v v t exp( ) τ      ] and from the decay times τv , the mass diffusion coefficient and the velocity changing collisions frequency have been determined. The comparison between the CMDS results and experimental results are presented and discussed.

In this work, the affection of the Dicke narrowing effect on the spectral shape of the 𝜈3 + 𝜈4 R(7)F1 transition of methane diluted in nitrogen was studied using the Hard- and the Soft- collision line-shape models. Room-temperature absorption spectra of CH4 broadened by N2 were measured at a wide range of pressure using a difference-frequency laser spectrometer. Measured spectra of the studied transition were then one-by-one fitted with the simple Voigt profile as well as the two line-shape models considered the Dicke narrowing effect at two different assumptions of velocity-changing collisions: hard- and soft- collisions. The obtained results confirmed that using these two models leads to better qualities of fit with respect to the Voigt profile. Pressure-dependences of the line-shape parameters were also observed for the considered transition. The results showed a good agreement with other studies.