Atmospheric observations of line intensity and half‐width in the rotation and ν 2 vibration‐rotation bands of water vapour

Curves of growth have been measured in the solar spectrum between 8 and 13 μ on five atmospheric water‐vapour lines, three in the rotation band and two in the ν 2 vibration‐rotation band. The water vapour in the path, from radiosonde data, was never less than 1 g cm –2 , so that it was possible to measure S 0 (the line intensity at T 0 = 273°K) and α 0 (the half‐width at p 0 = 1,000 mb) separately only for the weak line at 914.03 cm –1 , with errors of approximately 3 and 5 per cent respectively. For four strong lines at 871.32, 878.61, 1106.74 and 1111.53 cm –1 only the product S 0 α 0 could be obtained, with an estimated error of 8 per cent. The results of the rotation lines show reasonable agreement with theoretical values. Using theoretical values of α 0 , the normalizing factor n̈ for the two n̈ 2 lines are 0·0165 for 1106·74 and 0·0126 for 1111·53 cm –1 , which differ considerably from the overall normalizing factor 0·005 given for this band by Benedict et al. (1952) and show a slight dependence on the rotational quantum number J.