Consecutive and Parallel Dissociation of Energy-Selected Co(CO)3NO+ Ions

Abstract

Photoelectron photoion coincidence (PEPICO) spectroscopy has been used to investigate the dissociation dynamics of the cobalt tricarbonyl nitrosyl ion, Co(CO)3NO+. The ionization energy of Co(CO)3NO was measured from the threshold photoelectron spectrum to be 8.33 ± 0.04 eV. The dissociation of the molecular ion proceeds by two sequential carbonyl-loss steps and then a parallel carbonyl- or nitrosyl-loss step. The first two reactions were observed to be slow (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and the relative ion abundances (breakdown curves), 0 K onsets for the following fragment ions were determined: Co(CO)2NO+, 9.28 ± 0.02 eV; CoCONO+, 10.43 ± 0.02 eV; CoNO+, 12.00 ± 0.02 eV; CoCO+, 12.07 ± 0.02 eV. Combining these onsets with the experimental adiabatic ionization energy of Co(CO)3NO+, the three cobalt−carbonyl bond energies in Co(CO)xNO+ (x = 1−3) were determined along with the cobalt-nitrosyl bond energy in CoCONO+. Using a literature value for the [Co−CO]+ bond energy, the 0 K heats of formation of the above-mentioned molecular and fragment ions and of the neutral compound, Co(CO)3NO, were determined. Using these thermochemical data, the cobalt−nitrosyl bond energies were also derived for Co(CO)3NO+ and CoNO+. The latter is in good agreement with a theoretical literature value, while the first one explains why there is no observable NO loss from the molecular ion, Co(CO)3NO+. Room-temperature values of the heats of formation are also given using the calculated harmonic frequencies.