Absorption cross-sections in the vacuum ultra-violet III. Methane

Abstract

Cross-sections for the continuous absorption of radiation by methane in the wave-length range 1600 to 350A have been measured. The absorption is analyzed so as to distinguish between absorption leading to photo-dissociation processes and absorption due to photoionization. The main photo-ionization process is CH 4 +hv->CH 4 + -e - , and the photoionization 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-> CH 2 + H+e - The results are compared with calculations by Dalgamo. The paper includes an account of the technique of photographic spectrophotometry in the region 1100 to 200A.