The ionic states of iodobenzene studied by photoionization and ab initio configuration interaction and DFT computations

New valence electron photoelectron spectra of iodobenzene obtained using synchrotron radiation have been recorded. Ionization energies (IEs) determined using multi-configuration SCF calculation (MCSCF) procedures confirmed the adiabatic IE order as: (XB1)-B-2 < A(2)A(2) < (BB2)-B-2 < (CB1)-B-2. Although it is convenient to retain C(2)v labelling, there is an evidence that minor distortion to C-S symmetry occurs at the MCSCF level for the C state. The fifth ionization process shown to be D(2)A(1) exhibits dissociation to C6H5+ + I both in the experimental and theoretical studies. The calculated Franck-Condon vibrational spectral envelopes, including hot band contributions, for the first four ionic states reproduce the observed peak positions and intensities with reasonable accuracy. In order to simulate the observed spectra, different bandwidths are required for different states. The increase in the required bandwidths for the A(2)A(2) and (BB2)-B-2 states is attributed to internal conversion to lower-lying states. The presence of relatively high intensity sequence bands leads to asymmetry of each of the (XB1)-B-2 state bands. (C) 2015 AIP Publishing LLC.