Autoionization processes insymhyphen;trifluorobenzene and hexafluorobenzene: Studies involving threshold photoelectrons and ion fluorescence

摘要

Autoionization in large polyatomic molecules has been studied using synchrotron radiation as a variable energy VUV source. Threshold photoelectron spectra (TPES) ofsymhyphen;trifluorobenzene and hexafluorobenzene were measured over the 9ndash;29 eV range. Fluorescence quantum yields fgr;Fand lifetimes tgr; were determined for energy selected levels of the cations using the Thyphen;PEFCO technique in which coincidences are counted between threshold photoelectrons and ion fluorescence photons. The relative partial cross sections sgr;Xtilde;(E) and sgr;Btilde;(E) for threshold ionization to the nonfluorescingXtilde; and fluorescingBtilde; states of 1,3,5hyphen;C6F3H+3and C6F+6ions are determined. Peaks corresponding to bands of a Rydberg series converging to theCtilde; state of C6F+6are observed in the TPES of C6F6and result from threshold autoionization processes forming high vibrational levels of the ionBtilde; state. An intense underlying continuum in the TPES of 1,3,5hyphen;C6F3H3and C6F6is interpreted as being due to autoionization from superexcited neutral states to theXtilde; ground states of the corresponding cations. The autoionization processes are also discussed in terms of competition between autoionization and ionic core relaxation of superexcited states.