Hi Bojan
Quote:
Originally Posted by bojan
Hi sil,
It is simple:
At increased densities (and pressures) the spectral lines of gasses shift and widen... and that is why we have this "window" between UV and IR.
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The reason for the window is because there happen to be no strong molecular transitions eg vibration or rotation) matching the energy range of visible photons. (The temperature of the atmosphere is too low for atomic transitions)
It is mainly the molecular absorption bands in the spectrum of Ozone molecules in the UV and of water molecules in the IR that define the limits of the window. I expect if the window had been at some other part of the spectrum, life would have evolved to exploit this region instead.
Cheers
Robin