Dissociation Dynamics and Thermochemistry of Energy-Selected CpCo(CO)2+ Ions

Photoelectron photoion coincidence (PEPICO) spectroscopy has been used to investigate the dissociation dynamics of the cyclopentadienyl cobalt dicarbonyl ion, CpCo(CO) 2 + . The dissociation proceeds by the sequential loss of the two CO molecules. Both reactions proceed with no reverse activation energies and are slow near their dissociation onset. The 0 K onset was determined by modeling the measured dissociation rate constants with RRKM theory utilizing the variational transition state theory to locate the transition states. The ionization energy of CpCo(CO) 2 was measured from the threshold photoelectron spectrum to be 7.35 eV, which agrees with the literature value. The neutral CpCo(CO) 2 + gas-phase heat of formation of −117 ± 10 kJ/mol was determined from the liquid value by measuring the heat of vaporization of 52.12 ± 0.68 kJ/mol. The first Co−CO bond energy in the CpCo(CO) 2 + was found to be 1.53 ± 0.02 eV (148.1 ± 2 kJ/mol), giving a 298 K gas phase heat of formation of 857 ± 10 kJ/mol for CpCoCO + . The second Co−CO bond energy in CpCoCO + was measured to be 1.50 ± 0.02 eV (144.8 ± 2 kJ/mol), resulting in a 298 K gas phase heat of formation of CpCo + to be 1113 ± 10 kJ/mol.