Photoabsorption, photoionization, and neutral-dissociation cross sections of simple hydrocarbons in the vacuum ultraviolet range

The absolute photoabsorption cross sections, sigma(i), of CH4 and n-C4H10 have been measured in the photon energy range of the valence electrons using a double ionization chamber equipped with a metallic thin film window and synchrotron radiation as a continuous-wavelength light source. The absolute photoionization quantum yields, eta, of CH4 have been also measured, from which the photoionization cross sections, sigma(i), and neutral-dissociation cross sections, sigma(d), are obtained. The values of sigma(t) and eta of C-1-C-4 normal alkanes including our previous results for C2H6 and C3H8 have been compared in detail with those by the dipole-simulation method using the virtual photons. The gross features of the sigma(t) and eta values of these alkanes are discussed in terms of those as functions of the photon energy and the number of C atoms in an alkane molecule. (C) 2002 Elsevier Science B.V. All rights reserved.