Autoionization from the lone-pair orbitals of molecules containing iodine

Abstract

Autoionization to the lowest spin component of the ground state of the ion has been studied for the following alkyl iodides in the gas phase: CH3I, C2H5I, and nC3H7I. Measurements have been made using the constant ionic state (CIS) method for photon energies between the ionization potentials arising from the spin–orbit split lone-pair orbitals of iodine. To carry out the measurements, angle resolved photoelectron spectrometry has been coupled with a variable photon source extracted from synchrotron radiation. A series of broad resonances together with some sharp resonances are seen for each study and the results for each molecule in the series show strong similarity to one another, illustrating the localized atom-like character of the lone-pair orbital. There are strong differences found in the extent of the background, which is attributed to the higher density of states for the longer carbon chains. Most measurements were taken for the ground state vibrational level, but results are also presented for ionization to the ν2 excited vibrational state of CH3I+. New resonances, not seen for the ground vibrational state, are found and their origin discussed. CIS spectra on the I2 molecule are reported, which are in strong contrast to the alkyl iodides. Possible reasons for the differences are presented.