Partial channel photoionization cross sections of polyenes

Abstract

We present calculations of partial channel photoionization cross sections and photoelectron spectra of polyenes in the ultraviolet wavelength region. The dependences on molecular size, up to ${\mathrm{C}}_{16}$${\mathrm{H}}_{18}$, on photon energy, including He I and He II spectra, and on the particular ionization channel have been investigated using the independent-channel static exchange method. The channel dependence of the He I cross sections, which is quite strong for ethylene, diminishes, as the molecular length is increased, and becomes weak in the He II region. The energy dependence, which is strong in the He I region for all molecules and/or channels, is also insignificant for He II excitation, with the cross sections of all channels being close to each other. The cross sections are remarkably constant for the different \ensuremath{\pi} levels at any given photon energy. Spectral analyses for the first three smallest molecules---ethylene, butadiene, and hexatriene---show that the independent-channel approach is able to reproduce experimental data quite well.