Collision‐induced absorption by N₂ near 2.16 µm: Calculations, model, and consequences for atmospheric remote sensing

Classical molecular dynamics simulations (CMDS) are used for calculations of the collision‐induced absorption (CIA) by pure N 2 in the (2.1–2.2 µm) region of the first overtone band. They lead to reasonable (±15%) agreement with the only two laboratory measurements available, at 97 K and room temperature. Based on these experiment/theory comparisons, empirical corrections are made to the CMDS‐calculated CIA of pure N 2 in the 200–300 K temperature range. In addition, the contribution of N 2 ‐O 2 collisions is, in the absence of any laboratory measurement, calculated and a simple semiempirical model (the first of its kind) is built in order to predict the CIA of N 2 under Earth atmosphere conditions. This is successfully validated by comparisons with ground‐based atmospheric transmission spectra in the 2.1–2.2 µm region.