Bond dissociation energy determinations for MOC(CH3)2+ and MOC(CD3)2+, (M=Cr, Mn), using the continuous ejection and radiative association methods

摘要

The gas-phase ion-molecule reactions of Cr+ and Mn+ with acetone and acetone-d6 are studied with a Fourier transform ion cyclotron resonance mass spectrometer. Unimolecular dissociation rates of chemically activated complexes, (M(acetone)+)*, are obtained using the continuous ejection method. An inverse isotope effect is found for the Cr+/acetone/acetone-d6 system with kuniH/kuniD0.5, while the unimolecular dissociation rates are about the same for [MnOC(CH3)2+]* and [MnOC(CD3)2+]*. The bond dissociation energies, D°(Cr+-OC(CH3)2) = 1.82 ± 0.15 eV, D°(Cr+-OC(CD3)2) = 1.62 ± 0.15 eV, D°(Mn+-OC(CH3)2) = 1.65 ± 0.15 eV and D°(Mn+-OC(CD3)2) = 1.49 ± 0.15 eV, are derived from RRKM modeling with input parameters obtained from ab initio calculations. The radiative association reactions of Cr+ with acetone are also examined. The unimolecular dissociation rate constant of (Cr+?OC(CH3)2)*, derived from the RA kinetics, is compared with the CE measurement.