THE AERONOMIC DISSOCIATION OF WATER-VAPOR BY SOLAR-H LYMAN ALPHA-RADIATION

The photoabsorption cross sections of molecular oxygen and water vapor have been measured as a function of temperature at 0. 1 A intervals between 1214 and 1219 A. Over the width of the solar Lyman alpha line there is no fine structure apparent in the cross sections which were measured with 0. 05 A resolution. A large wavelength and temperature dependence is seen in the molecular oxygen cross sections, but the variations are much smaller in the case of water vapor. The measured cross sections are used in calculations of the rate of photodissociation of atmospheric water vapor by solar Lyman alpha radiation, taking full account of both the temperature and wavelength dependences.