A study of the photoionisation dynamics of chloromethane and iodomethane

Angle resolved valence shell photoelectron spectra of chloromethane and iodomethane have been recorded using synchrotron radiation in the photon energy range 14-120 eV. These have allowed photoelectron angular distributions and branching ratios to be determined not only for the main bands associated with the single-hole states but also for the satellite structure due to many-electron effects. The continuum multiple scattering approach has been used to calculate photoelectron asymmetry parameters and branching ratios for the valence orbitals of CH3Cl and CH3I, and also for the I 4d subshell. A comparison between the experimental data and the theoretical predictions has enabled the influence of Cooper minima, shape resonances and intershell coupling to be assessed. The asymmetry parameters and branching ratio for the spin-orbit split components of the CH3I+X˜2E state have been measured and exhibit a spectral behaviour almost identical to that of the corresponding data for the Xe 5p3/2 and 5p1/2 levels. The many-body Green's function approach has been employed to evaluate the ionisation energies and spectral intensities of all valence states and the results have facilitated an interpretation of the satellite structure. The I 4d shake-up, shake-off and Auger spectra of iodomethane have been recorded and many of the Auger peaks have been assigned using previously determined ionisation energies of doubly charged valence states.