Question

absorption spectra of water at microwave frequencies

Answer 1

Water absorbs over a wide range of electromagnetic radiation with rotational transitions and intermolecular vibrations responsible for absorption in the microwave (~1 mm - 10 cm wavelength) and far-infrared (~10 µm - 1 mm), intramolecular vibrational transitions in the infrared (~1 µ- 10 µ) and electronic transitions occurring in the ultraviolet region (< 200 nm).

 

 

 

The water absorption spectrum is very complex. Water's vapor spectroscopy (including microwave [3176]) has been reported [348a] and recently reviewed [348b]. The water molecule may vibrate in a number of ways. In the gas state, the vibrations [607] involve combinations of symmetric stretch (v1), asymmetric stretch (v3) and bending (v2) of the covalent bonds with absorption intensity (H216O) v1;v2;v3 = 0.07;1.47;1.00 [8]. As shown right, there is significant isotope effects with the frequencies in H2O are higher than those in D2O and T2O; the ratios between H2O, D2O, and T2O being approximately the square root of the D:H or T:H atomic mass ratios. The stretch vibrations of HDO refer to the single bond vibrations, not the combined movements of both bonds. Gas phase rotations [1701] are complex and are combined with these vibrations. The lowest ortho-para transitions are given elsewhere.