Variable-Energy Photoelectron Spectroscopy of CpM(CO)2 (M = Co, Rh, Ir): Molecular Orbital Assignments and an Evaluation of the Difference in Ground-State Orbital Characters

Abstract

Photoelectron (PE) spectra with variable photon energy have been recorded between 21 and 70 eV using He I, He II, and synchrotron radiation for the cobalt, rhodium, and iridium complexes CpM(CO)2, where Cp is η5-cyclopentadienyl. The spectra have been assigned on the basis of Xα-SW molecular orbital (MO) calculations for the ground-state CpM(CO)2 molecules and by consideration of trends in photoelectron band intensities as a function of the energy of the radiation used. Photoionization cross sections (σ) have been calculated for the valence ionizations of the three molecules, using both the Xα-SW and Gelius methods. The theoretical branching ratios (σi/∑σ) from both theoretical methods have been compared with the observed branching ratios (Ai/∑A) between 21 and 70 eV. Our assignment (from the He I and He II spectra and the agreement between theoretical and observed branching ratios between 21 and 70 eV) gives a similar ordering of ionization potentials (IP's) for CpCo(CO)2 and CpRh(CO)2 with those reporte...