Electromagnetic absorption by water

Absorption spectrum (attenuation coefficient vs. wavelength) of liquid water (red),[1][2][3] atmospheric water vapor (green)[4][5][6][4][7] and ice (blue line)[8][9][10] between 667 nm and 200 μm.[11] The plot for vapor is a transformation of data Synthetic spectrum for gas mixture 'Pure H2O' (296K, 1 atm) retrieved from Hitran on the Web Information System.[6]
Liquid water absorption spectrum across a wide wavelength range[missing source]

The absorption of electromagnetic radiation by water depends on the state of the water.

The absorption in the gas phase occurs in three regions of the spectrum. Rotational transitions are responsible for absorption in the microwave and far-infrared, vibrational transitions in the mid-infrared and near-infrared. Vibrational bands have rotational fine structure. Electronic transitions occur in the vacuum ultraviolet regions.

Liquid water has no rotational spectrum but does absorb in the microwave region. Its weak absorption in the visible spectrum results in the pale blue color of water.

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