Neutral Cobalt−Carbonyl Bond Energy by Combined Threshold Photoelectron Photoion Coincidence and He(I) Photoelectron Spectroscopy

Abstract

Ultraviolet photoelectron (PE) spectroscopic experiments were carried out on cyclopentadienyl cobalt dicarbonyl CpCo(CO) 2 (I) using a pyrolysis inlet system. Above a certain temperature this molecule loses a carbonyl group, resulting in the 16-electron molecule CpCoCO (II). By subtracting the PE spectrum of (I) from the mixed experimental spectrum, the PES of (II) was obtained. Adiabatic and vertical ionization energies (IEs) were also determined. By using a thermodynamic cycle, which included the appearance energy of CpCoCO + determined in an earlier threshold photoelectron photoion coincidence (TPEPICO) experiment, the dissociation energy of CpCOCO...CO was obtained to be 1.91 ′ 0.05 eV. Quantum-chemical calculations were also carried out to help the reassignment of the photoelectron spectrum of (I) and to help establish a reliable value of the adiabatic IE of (II).