The shape of the continuous β -spectrum of thorium C. C'

Cross-sections for the continuous absorption of radiation by methane in the wave-length range 1600 to 350 angstrom have been measured. The absorption is analyzed so as to distinguish between absorption leading to photo-dissociation processes and absorption due to photo-ionization. The main photo-ionization process is CH$_{4}$+hv$\rightarrow $CH$_{4}^{+}$+e$^{-}$, and the photo-ionization cross-section is measured for free electron energies from 0 to about 20 eV. Little evidence is found for processes such as CH$_{4}$+hv$\rightarrow $CH$_{3}^{+}$+H+e$^{-}$. The results are compared with calculations by Dalgarno. The paper includes an account of the technique of photographic spectrophotometry in the region 1100 to 200 angstrom.