AN EMPIRICAL MODEL FOR THE INFRARED COLLISION INDUCED ABSORPTION BAND OF $N_{2}$ NEAR 4.3 $\mu$m

Author Institution: LPMA, Universit\'{e} de Paris Sud (b\bar{a}t. 350); National Institute of Standards and Technology, Universit\'{e} de Paris Sud (b\bar{a}t. 350); Institute of Atmospheric Optics, Academy of Sciences; National Institute of Standards and Technology, Academy of SciencesVery accurate measurements of collision induced absorption by pure nitrogen have been made in the 0 - 10 atm and 230 - 300K pressure and temperature ranges, respectively, using a BOMEM Fourier transform spectrometer with a resolution of $0.5 cm^{-1}$. The measurements are, in general, in good agreement with those reported previously but are more precise. Small weak features have been found superimposed on the broad $N_{2}$ continuum which previously had been observed only at very low temperatures. These features have negligible temperature dependence and, at this time, their origin is not known. Available data in the range of temperature from 190 to 300K have been used to derive a simple empirical model suitable for calculating atmospheric absorption. Assuming an atmospheric composition of $21%O_{2}+79%N_{2}$, the absorption coefficient of $N_{2}$ in the atmosphere can be expressed as: $$ \alpha^{Atm}_{N_{2}}(\sigma,P,T)=\left\[p\frac{273}{T}\right\]^{2}[0.8387+0.0754\frac{T}{T_{0}}]B^{0}_{N_{2}N_{2}}(\sigma)\exp[B^{0}_{N_{2}N_{2}}(\sigma)(\frac{1}{r_{0}}-\frac{1}{T})] $$ where the reference temperature, $T_{0}$, is 296K and $B^{0}_{N_{2}-N_{2}}(\sigma)$ and $B^{0}_{N_{2}-N_{2}}(\sigma)$ are empirical fitting parameters