A study of submillimetre atmospheric absorption using the HCN maser

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 9; no. 6; pp. 809 - 824
• Main Authors: Burroughs, W.J., Jones, R.G., Gebbie, H.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.1969
• ISSN: 0022-4073; 1879-1352
• DOI: 10.1016/0022-4073(69)90077-6

A study of water vapour absorption at two submillimetre wavelengths (337 μm and 311 μm) has been made as a function of foreign gas pressure using A, CH 4, N 2 and CO 2 as the broadeners in order to explain excessive absorption in the atmospheric “window” regions. As an extension of this work the absorption coefficient of water vapour alone was measured as a function of pressure and temperature. From an analysis of the ratio of the absorption coefficients at the two wavelengths, the anomalous absorption has been explained in terms of three contributions. 1. 1. A background absorption which is independent of foreign gas broadening. This is ascribed to two-body collisions in water vapour which may be explained in terms of a dimeric form of the water molecule having a binding energy of (5·2±1·5) kcal mol -1. 2. 2. A modification of the line shape in the far wings which is dependent upon the foreign gas pressure and quadrupole moment. This effect is consistent with a two body quadropole collision-induced background absorption. 3. 3. A three-body effect which is related to the quadropole moment of the foreign gas used to broaden the water vapour lines.