The Schumann-Runge bands of molecular oxygen between 175 nm and 205 nm cover a spectral region of great importance for the effect of solar radiation in the middle atmosphere. The highly structured absorption cross sections that can be computed with good accuracy lead to prohibitive computer resources, however, when they have to be used in complex atmospheric models. Although various approximations have been developed, another approach is proposed to avoid spurious effects, even when the new approximations are used outside of their validity range, corresponding to a solar attenuation of the order of 10-10. Comparisons between exact computations and present approximations lead to satisfactory agreement.