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Generation of vacuum ultraviolet radiation by plasma nonlinearities AIP Conf. Proc. 90, 224 (1982); 10.1063/1.33764Photoionization quantometer for absolute intensity measurements of vacuum ultraviolet and soft xray radiation from laser plasma Rev. Sci. Instrum. 52, 16 (1981);

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Absorption cross sections of methane and ammonia for electromagnetic radiation in the range from 1300 A to 374 were obtained with a two-meter radius of curvature, grazing incidence vacuum spectrograph. For methane 85 wavelengths were measured. Starting from σ = 14 Mb (1 Mb = 10—18 cm2) at 1300 A, the absorption first increased slowly and then rose more rapidly to a maximum of σ = 56 Mb at 960±278 A corresponding to the first ionization potential of methane. The absorption then decreased gradually to 14 Mv at 374 A. The total f-value pertaining to the transitions of 2p-electrons was found to be 6.1. For ammonia, 100 wavelengths were measured. Band absorption appeared at longer wavelengths. The continuous absorption began near 1210 A and extended to the shorter wavelengths. The structure of the absorption contour suggested the existence of two ionization continua: a weaker one with maximum σ = 21 Mb at 1130±20 A and a larger one with its maximum of 34 Mb at 730±20 A. These two maxima corresponded to the ionization limits of the outer electrons of ammonia. The total f-value was found to be 5.9.